A retaining member which is mounted on an end part of a shaft (9a, 71) supported by a holding member (40, 70), and prevents the shaft from coming off from the holding member or prevents a rotary body mounted around the shaft from coming off, the retaining member comprising: an inner circumferential portion which is ring-shaped; and a plurality of engagement claws which project from the inner circumferential portion, and engage with an engagement groove formed in an outer peripheral surface of the shaft (9a, 71), the retaining member being integrally formed of an elastically deformable material, characterized in that the retaining member further comprises: an outer circumferential portion which is ring-shaped and disposed outside the inner circumferential portion in a radial direction; a linkage portion which connects the inner circumferential portion and the outer circumferential portion to each other in the radial direction; and a slit which is formed on a side opposite from the linkage portion with a center of the inner circumferential portion located between the slit and the linkage portion, and cuts the inner circumferential portion in the radial direction, in that, by the engagement claws contacting an end portion of the shaft (9a, 71), the inner circumferential portion is caused to be elastically deformed to cause the slit to become wide open, and the engagement claws are pushed in an axial direction of the shaft (9a, 71) while simultaneously being withdrawn outward in the radial direction, and in that, when the engagement claws reach the engagement groove formed in the outer peripheral surface of the shaft, the inner circumferential portion is caused by recovery force to shrink inward in the radial direction to cause the engagement claws to engage with the engagement groove, and thereby the retaining member is mounted on the shaft (9a, 71). an inner circumferential portion which is ring-shaped; and a plurality of engagement claws which project from the inner circumferential portion, and engage with an engagement groove formed in an outer peripheral surface of the shaft (9a, 71), the retaining member being integrally formed of an elastically deformable material, characterized in that the retaining member further comprises: an outer circumferential portion which is ring-shaped and disposed outside the inner circumferential portion in a radial direction; a linkage portion which connects the inner circumferential portion and the outer circumferential portion to each other in the radial direction; and a slit which is formed on a side opposite from the linkage portion with a center of the inner circumferential portion located between the slit and the linkage portion, and cuts the inner circumferential portion in the radial direction, an outer circumferential portion which is ring-shaped and disposed outside the inner circumferential portion in a radial direction; a linkage portion which connects the inner circumferential portion and the outer circumferential portion to each other in the radial direction; and a slit which is formed on a side opposite from the linkage portion with a center of the inner circumferential portion located between the slit and the linkage portion, and cuts the inner circumferential portion in the radial direction, in that, by the engagement claws contacting an end portion of the shaft (9a, 71), the inner circumferential portion is caused to be elastically deformed to cause the slit to become wide open, and the engagement claws are pushed in an axial direction of the shaft (9a, 71) while simultaneously being withdrawn outward in the radial direction, and in that, when the engagement claws reach the engagement groove formed in the outer peripheral surface of the shaft, the inner circumferential portion is caused by recovery force to shrink inward in the radial direction to cause the engagement claws to engage with the engagement groove, and thereby the retaining member is mounted on the shaft (9a, 71).