PURPOSE: To eliminate the need for troublesome trial copying operation during the exposure adjustments of a photosensitive body and to easily execute adjustments for manufacture and maintenance by providing a switching means which switches and adjusts the brightness of an exposure lamp in plural stages according to the sensitivity of the photosensitive body.

CONSTITUTION: An exposure lamp control part 4 starts turn-on control over the exposure lamp 1 with an exposure command from a switch 12 associated with copying operation to perform feedback control over the brightness of the exposure lamp 1 corresponding to a set voltage Vs and also make corrections based upon the temperature of the photosensitive drum and the quantity of copies. Then, a brightness value set by a brightness setter 9 is corrected by a changeover switch circuit 11 with a bias. When a changeover switch SW is switched, the adjustment to a switching position corresponding to the sensitivity of the photosensitive drum is executed and switching operation is performed according to the classes of sensitivity of the photosensitive drum mounted on the main device body.