An optical reproducing device is provided with predetermined length mark signal measurement means which measures amplitude values of a 2T mark and an 8T mark, which are a short reproducing power control mark and a long reproducing power control marks, respectively, from information data recorded in an magneto-optical disk. Reproducing power of a light beam is controlled by a laser power control circuit, based on the amplitude values of the 2T mark and the 8T mark. The predetermined length mark signal measurement means detects a specific pattern including the 2T mark from a bit arrangement pattern of the information data, and measures the amplitude value of the 2T mark correponding only to the 2T mark included in the specific pattern. This structure can provide an optical reproducing device which can maintain the reproducing power at an optimum value and reduce the probability of reading errors, without reducing the utilization ratio of an optical recording medium.