An image forming apparatus comprising: a photosensitive drum configured to hold a toner image to be transferred to a sheet member; shaft portions (65C, 75C) connected to both ends in an axial direction of the photosensitive drum and projecting outward in the axial direction from a center of the photosensitive drum; support portions (71, 72) having shaft holes (71A, 72A) through which the shaft portions (65C, 75C) are inserted, and configured to rotatably support the shaft portions (65C, 75C); bush members interposed between inner surfaces of the shaft holes (71A, 72A) and outer circumferential surfaces of the shaft portions (65C, 75C), and each formed in an arc shape having a slit extending in the axial direction; and positioning portions provided in the support portions (71, 72) and configured to position the bush members at predetermined positions in a circumferential direction, characterized in that at least one rib extending in the axial direction is formed in an outer circumferential surface of each bush member, each positioning portion is an engagement groove which is formed at a position corresponding to the rib in an inner circumferential surface of the shaft hole (71A, 72A), and which is configured to be engaged with the bush member in the circumferential direction, with the rib inserted in the engagement groove, a hook-shaped portion bent orthogonally in the circumferential direction is formed at one end in the axial direction of the rib, and when the bush member is inserted through the shaft hole (71A, 72A), the rib is inserted in the engagement groove, and the hook-shaped portion is engaged with an edge portion in the circumferential direction of the engagement groove, thereby functioning to prevent drop off. a photosensitive drum configured to hold a toner image to be transferred to a sheet member; shaft portions (65C, 75C) connected to both ends in an axial direction of the photosensitive drum and projecting outward in the axial direction from a center of the photosensitive drum; support portions (71, 72) having shaft holes (71A, 72A) through which the shaft portions (65C, 75C) are inserted, and configured to rotatably support the shaft portions (65C, 75C); bush members interposed between inner surfaces of the shaft holes (71A, 72A) and outer circumferential surfaces of the shaft portions (65C, 75C), and each formed in an arc shape having a slit extending in the axial direction; and positioning portions provided in the support portions (71, 72) and configured to position the bush members at predetermined positions in a circumferential direction, characterized in that at least one rib extending in the axial direction is formed in an outer circumferential surface of each bush member, each positioning portion is an engagement groove which is formed at a position corresponding to the rib in an inner circumferential surface of the shaft hole (71A, 72A), and which is configured to be engaged with the bush member in the circumferential direction, with the rib inserted in the engagement groove, a hook-shaped portion bent orthogonally in the circumferential direction is formed at one end in the axial direction of the rib, and when the bush member is inserted through the shaft hole (71A, 72A), the rib is inserted in the engagement groove, and the hook-shaped portion is engaged with an edge portion in the circumferential direction of the engagement groove, thereby functioning to prevent drop off.