An image forming apparatus includes a photoconductor drum in which a first gear portion is formed on the axis of rotation and on which an electrostatic latent image corresponding to a toner image is formed by a rotation in a circumferential direction; a developing roller which is set correspondingly to the photoconductor drum, and makes visible the electrostatic latent image formed on the photoconductor drum thereby to form a toner image; and a photoconductor drive shaft having a second gear portion engaging with the first gear portion and formed on an axis of rotation, which gears with the photoconductor drum on the same axis and rotation-drives this photoconductor drum. Further, in at least either of the first gear portion and the second gear portion, an axial length of a part of gear teeth constituting the gear portion is different from axial lengths of other teeth.