PURPOSE: To perform invariably stable and accurate information recording by forming pits of prescribed size at prescribed intervals during the forming period of pits which correspond to pit data "0" or "1", and thus representing the data as a string of pits.

CONSTITUTION: Information data to be recorded are stored temporarily in a buffer memory 1, and MFM modulation 3 is imposed on the data; and a driving circuit 4 generates pulse signals which correspond to pit data "0" and "1" in the MFM-modulated data string, and those pulse signals are inputted to a head B. An optical disk A is irradiated with laser light from a semiconductor laser element 5 to form a string of pits, thus performing information recording. The modulation of the irradiation light is switched selectively to enough intensity to form pits on the optical disk A and enough intensity to obtain low-level reflected light which does not contribute to the pit formation. The time-width variation of the MFM-modulated signal is recorded as variation in the number of pits of the same size formed successively at prescribed intervals.