PURPOSE: To reduce fluctuation of rotation speed of a driving motor by changing a driving frequency of an image formation driving motor in an apparatus for forming an image on a fed material.

CONSTITUTION: An original on a platen 5 is illuminated through a slit, and the reflected light is projected on a rotating 3-layer screen 1 to form an electrostatic latent image. A secondary electrostatic latent image is formed on an insulating drum 7 surface by transferring this primary image with a modulation charger 8. The secondary image is developed with a developer 8, the toner image is transferred on a transfer sheet 10 fed from a cassette 52 or a lift deck 53, the sheet is conveyed to a fixing device 13, fixed here, and ejected to a sorter 18 or a tray 14. The rotation driving power of a sheet feed roller 9 and a register roller 41 is transmitted through a clutch from a motor for driving the screen 1 and the drum 7. At the same time as the clutch is connected, the frequency for driving the motor is raised, e.g., from 53Hz to 56Hz. As a result, fluctuation of the rotation of the drum 7 is reduced, and an image of good quality can be obtained.