PURPOSE: To obtain an image recorded with dots by equal intervals with uniform density, by differentiating a galvanomirror driving signal with respect to time, controlling intensity of laser beams by this differentiated output, and at the same time, controlling clock frequency.

CONSTITUTION: Laser beams emitted from a gas laser 1 are passed through a photomodulator 2 and a converging lens 3, and projected to galvanomirror 4. This mirror 4 resonates at high speed in accordance with a driving signal sent from a drive circuit 11 to scan a drum 5. On the other hand, output of the circuit 11 is rectified through a differentiator 12, its output is applied to a photomodulator driving circuit 13 to control the photomodulator and to change laser beam intensity. Output of the differentiator 12 is also applied to a clock generator 14 to change clock frequency corresponding to the speed of scanning the photoconductive drum surface, thus permitting a dot recorded image recorded by equal intervals without uneven density to be formed.