PURPOSE: To form high definition colored pictures, by providing a means which individually adjusts the light emitting power of each laser beam radiated from plural laser units in accordance with the sending-out timing of beam detect signals.

CONSTITUTION: Comparators COM1WCOM4 compare the light quantity levels of laser beams made incident on BD signal generating units 54C, 54M, 54Y, and 54BK with previously set reference levels and, when the light quantity levels exceed the reference levels, input beam detect signals BD1WBD4 to the input ports IN1WIN4 of a control section COT. A counter CNT starts the counting of reference clocks CL2 from an oscillator X outputted from the clockout CLOUT of the control section COT by using the first inputted beam detect signal among the beam detect signals BD1WBD4 outputted from the input ports IN1WIN4 and outputs count signals to the control section synchronously to the successively inputted beam detect signal outputs. Therefore, high definition colored pictures can be formed.