An attenuation-amount adjusting circuit includes: a light irradiating unit that alternately irradiates a laser beam of a writing level and a laser beam of a readout level on an optical disk that has a groove formed by a wobble pattern and plural markers indicating physical positions in the groove; a light receiving unit that receives reflected light of the laser beam irradiated on the optical disk and converts the reflected light into a reproduction signal; and a writing-waveform attenuating unit that attenuates an amplitude level of a writing waveform corresponding to the reflected light of the laser beam of the writing level in the reproduction signal according to a position from a rising edge of the writing waveform.