PURPOSE: To keep a fixed recording bit width to perform recording regardless of the nature and form of an information signal, by changing the light intensity in response to the information signal and after discriminating the length of light irradiating time (light duration) and then varying the exposure intensity.

CONSTITUTION: A light intensity control circuit 30 is provided between a signal source 21 and a light modulator 22, and the modulation degree of the modulator 22 is controlled in response to the pulse width of the information signal supplied from a signal source 21. Thus the light intensity is changed. In other words, a recording beam 19 is radiated from a light source 20 and then modulated by the modulator 22. In this case, the signal supplied from the source 21 produces the voltage corresponding to the pulse width by a pulse width discriminator 41 for a period of pulse duration and then controls the gain of a variable gain amplifier 42. While the recording information signal is delayed by a delay line 43 and the discriminator 41 for a period needed for decision of the pulse width. The amplifier 42 functions to reduce the gain when the pulse width is large. As a result, the recording bit width is controlled the fixed value.