An image forming apparatus includes a transfer belt, a photoconductor drum, and a transmission member. The transfer belt includes a transfer surface. The photoconductor drum faces the transfer surface of the transfer belt in an attachment state where the photoconductor drum is attached to an apparatus main body. The transmission member is attached to a drum end of the photoconductor drum on the insertion direction side and transmits an input rotational driving force to the photoconductor drum. The transmission member includes a flange and a gear. The flange is larger than the photoconductor drum in outer diameter. The gear projects from the flange in the insertion direction with teeth being formed on an outer circumferential surface of the gear, the teeth receiving the rotational driving force. The gear is larger than the photoconductor drum and smaller than the flange in outer diameter.