IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide a drive transmission device that makes the angle at which a drive gear engages the idler gear and the angle at which a transmission gear engages the idler gear optimum, thereby preventing color drift.SOLUTION: An image forming apparatus comprises first and second driving parts, each of which has: a transmission gear rotated by a driving source; an idler gear rotated by engaging the transmission gear; and a drive gear configured to transmit driving force to the corresponding photoreceptor drum by engaging the idler gear. The first and second driving parts transmit driving force to the corresponding first and second photoreceptor drums. Where an angle from the point at which the idler gear and the transmission gear engage to the point at which the idler gear and the drive gear engage is defined as the engaging angle of the idler based on the rotation center of the idler gear, the angle at which the first driving part engages the idler gear is substantially equal to the angle at which the second driving part engages the idler gear. The first driving part and the second driving part are almost identical in the rotation phase of the idler.