IMAGE FORMING APPARATUS

PURPOSE:To obtain an image forming apparatus capable of always keeping the proportional relation between the light output on a photosensitive surface and the gradation level of multi-gradation image data even when the environmental temp. of a laser diode fluctuates. CONSTITUTION:A correction circuit is formed from a correction table 30, a voltage detection circuit 31, a light output detection circuit 32 and a digital circuit 33. The circuit 31, 32 detect the threshold current of a laser diode 1. The digital control part 33 stores the correlation data of the threshold current and the case temp. of the laser diode 1, the corrlation data of the peak oscillation wavelength of the laser diode 1 and the case temp. and correction table data. The correction table data is formed at every oscillation wavelength of the laser diode 1. The correction table 30 corrects the current value to a laser diode driving circuit 5 on the basis of the correction table data so that the light output on a photosensitive surface and a gradation level become proportional relation.