A controller calculates a modulation degree of an RF signal provided from a signal processor, and supplies a record power that exhibits the calculated modulation degree matching with a target modulation degree as an optimum record power to a laser driver. More specifically, a modulation degree measuring portion measures the modulation degree of a signal of a predetermined frequency among the RF signals, e.g., a signal of 11T among signals of 3T-11T. The modulation degree measuring portion measures the modulation degree for each record power in OPC. The power determining portion determines a target record power such that the modulation degree measured by the modulation degree measuring portion attains the target modulation degree set by an OPC executing portion.