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A grounding structure includes a rotation shaft and a grounding member. The rotation shaft has a non-circular cross section, and rotates. The grounding member is attached to the rotation shaft to electrically communicate with the rotation shaft, and rotates together with the rotation shaft. The grou

A grounding structure includes a rotation shaft and a grounding member. The rotation shaft has a non-circular cross section, and rotates. The grounding member is attached to the rotation shaft to electrically communicate with the rotation shaft, and rotates together with the rotation shaft. The grounding member includes a first grounding portion, a grounding retainer and a second grounding portion. An outer shape of the first grounding portion is a circular shape. The grounding retainer is provided on a side of the first grounding portion in a shaft direction of the rotation shaft, and has an outside diameter being larger than an outside diameter of the first grounding portion. The second grounding portion is elastically held in contact with the first grounding portion.

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1. A grounding structure comprising: a rotation shaft that has a non-circular cross section, and that rotates; anda grounding member that is attached to the rotation shaft to electrically communicate with the rotation shaft, and that rotates together with the rotation shaft, whereinthe grounding mem

1. A grounding structure comprising: a rotation shaft that has a non-circular cross section, and that rotates; anda grounding member that is attached to the rotation shaft to electrically communicate with the rotation shaft, and that rotates together with the rotation shaft, whereinthe grounding member includes: a first grounding portion of which outer shape is a circular shape;a grounding retainer that is provided on a side of the first grounding portion in an axial direction of the rotation shaft, and that has an outside diameter that is larger than an outside diameter of the first grounding portion along an entirety of an outer periphery of the first grounding portion, wherein the grounding retainer completely surrounds the outer periphery of the first grounding portion when viewed along the axial direction of the rotation shaft; anda spring member that is elastically held in contact with the first grounding portion of the grounding member, wherein the grounding member is biased toward of the rotation shaft by the spring member. 2. The grounding structure of claim 1, wherein the grounding member is conductive in its entirety, andthe grounding member includes a restraint portion which restrains the grounding member from moving in the axial direction of the rotation shaft. 3. The grounding structure of claim 2, wherein the first grounding portion is sandwiched between two grounding retainers that form a circumferential groove; andeach of the two grounding retainers includes a convex stripe as the restraint portion, and the convex stripe is present on an outer side of the circumferential groove in the axial direction of the rotation shaft. 4. A sheet transport apparatus comprising; a grounding structure comprising: a rotation shaft that has a non-circular cross section, wherein the rotation shaft transports a sheet and rotates; anda grounding member that is attached to the rotation shaft to electrically communicate with the rotation shaft, and that rotates together with the rotation shaft, wherein the grounding member includes: a first grounding portion having a circular outer shape;a grounding retainer that is provided on a side of the first grounding portion in an axial direction of the rotation shaft, and that has an outside diameter that is larger than an outside diameter of the first grounding portion along an entirety of an outer periphery of the first grounding portion, wherein the grounding retainer completely surrounds the outer periphery of the first grounding portion when viewed along the axial direction of the rotation shaft; anda spring member that is elastically held in contact with the first grounding portion of the grounding member, wherein the grounding member is biased toward the rotation shaft by the spring member. 5. An image formation apparatus comprising: an image formation section that forms an image on a sheet to be transported; andthe sheet transport apparatus of claim 4. 6. The grounding structure of claim 1, wherein the first grounding portion and the grounding retainer are integrally formed, and comprises a single conductive material. 7. The grounding structure of claim 1, wherein the conductive material is a resin. 8. A grounding structure comprising: a rotation shaft that has a non-circular cross section and includes a protrusion portion that protrudes in a direction perpendicular to an axial direction of the rotation shaft, and the rotation shaft rotates; anda grounding member that is attached to the rotation shaft to electrically communicate with the rotation shaft, and that rotates together with the rotation shaft, whereinthe grounding member includes: a first grounding portion of which outer shape is a circular shape;a grounding retainer that is provided on a side of the first grounding portion in a the axial direction of the rotation shaft, and that has an outside diameter that is larger than an outside diameter of the first grounding portion along an entirety of an outer periphery of the first grounding portion, wherein the grounding retainer completely surrounds the outer periphery of the first grounding portion when viewed along the axial direction of the rotation shaft, and wherein the grounding retainer has a shaft hole having a notch formed through the grounding retainer in an axial direction of the grounding retainer; anda second grounding portion that is elastically held in contact with the first grounding portion. 9. The grounding structure of claim 8, wherein the grounding member is conductive in its entirety, andthe grounding member includes a restraint portion which restrains the grounding member from moving in the axial direction of the rotation shaft. 10. The grounding structure of claim 9, wherein the first grounding portion is sandwiched between two grounding retainers that form a circumferential groove; andeach of the two grounding retainer includes a convex stripe as the restraint portion, each convex stripe is formed on an outer side of the circumferential groove in the axial direction of the rotation shaft. 11. A sheet transport apparatus comprising the grounding structure of claim 1, wherein the rotation shaft transports a sheet, and the grounding structure grounds the rotation shaft. 12. An image formation apparatus comprising: an image formation section that forms an image on a sheet to be transported; andthe sheet transport apparatus of claim 11. 13. The grounding structure of claim 8, wherein the notch extends toward the outside diameter of the grounding retainer. 14. The grounding structure of claim 8, wherein the protrusion portion of the rotation shaft fits into the notch of the shaft hole of the grounding retainer. 15. A grounding structure comprising: a rotation shaft that has a non-circular cross section, and that rotates; anda grounding member that is attached to the rotation shaft to electrically communicate with the rotation shaft, and that rotates together with the rotation shaft, whereinthe grounding member includes: a first grounding portion of which outer shape is a circular shape;a grounding retainer that is provided on a side of the first grounding portion in a shaft direction of the rotation shaft, and that has a larger outside diameter larger than an outside diameter of the first grounding portion;a second grounding portion that is elastically held in contact with the first grounding portion;wherein the first grounding portion is sandwiched between two grounding retainers that form a circumferential groove; andwherein each of the two grounding retainers includes a convex stripe as the restraint portion, and the convex stripe is present on an outer side of the circumferential groove in an axial direction of the rotation shaft. 16. The grounding structure of claim 1, wherein the grounding retainer is provided on both sides of the first grounding portion in the axial direction of the rotation shaft. 17. The grounding structure of claim 4, wherein the grounding retainer is provided on both sides of the first grounding portion in the axial direction of the rotation shaft. 18. The grounding structure of claim 8, wherein the grounding retainer is provided on both sides of the first grounding portion in the axial direction of the rotation shaft.