An image forming apparatus, having a first developing roller, a second developing roller, a third developing roller, a fourth developing roller, a first photosensitive drum, a second photosensitive drum, a third photosensitive drum, a fourth photosensitive drum, a motor, a first output gear, a first gear train, and a second gear train, is provided. The first output gear is arranged coaxially with the motor and outputs a driving force from the motor. The first gear train includes a first intermediate gear meshing with the first output gear and transmits the driving force from the motor through the first output gear to the first, second, third, and fourth developing rollers. The second gear train includes a second intermediate gear meshing with the first output gear and transmits the driving force from the motor through the first output gear to the first, second, third, and fourth photosensitive drums.