PURPOSE: To control the quantity of light of an exposure lamp by detecting and integrating the quantity of light of the exposure lamp or a monitor lamp controlled at the same timing, and controlling the timing of the switching of an AC power source with pulse width corresponding to the integral value.

CONSTITUTION: A halogen lamp 31 for original exposure and a halogen lamp 32 for monitoring are supplied with an AC input 33 through a filter 34 and a lamp driving circuit 35. The quantity of light of the lamp 32 is detected by an output monitoring circuit 37 consisting of a photodiode and converted by an integrating circuit 38 into a direct current, and a monitor signal after the temperature compensation of an adding circuit 39 is supplied to an error amplifier 42. An error signal based upon a reference signal from a dimming circuit 43 is supplied to a pulse width modulating circuit 46. The input 33, on the other hand, is supplied to an electric power source circuit 49 and the circuit 46 applies a detected pulse signal to a trigger circuit 36 through a detecting circuit 54 to trigger the bilateral thyristor in the circuit 35, controlling the quantities of light of lamps 31 and 32. Thus, variation in the quantity of light is suppressed to obtain a copied image of high quality.