PURPOSE: To attain a high precise image formation by detecting a light emitting quantity from a laser element, carrying out the variable control of the temp. of the laser element based on an outputting signal and correcting the fluctuations of the light emitting quantity of the laser element.

CONSTITUTION: A constant current flows into the laser element 101 by a current control means 108, and laser beam corresponding to the current is outputted from the laser element 10. A part of the light emitting quantity is detected by a photodiode 102, and the outputting signal is subjected to current/voltage conversion by resistor 110, and inputted into one side of a comparator 105, and a reference signal on the target value of optical output from the laser element 101 is inputted into the input end of the other side from a reference power source 104. Then, the comparator 105 compares a signal outputted from the photodidode 102 with the reference signal, the laser element 103 is heated or cooled by a temp. control means 103 based on the compared result, and the light emitting quantity from the laser element 101 is adjusted. Thus, the high precise image formation can be attained.