Provision of a displacement sensor, which detects an amount of shift at an objective lens, and a controller, which adjusts an emitted power based on a value measured by the displacement sensor and compensation data stored in a memory, permits detection by the displacement sensor of the amount of shift at the objective lens as necessary during recording of data, and the controller is capable of causing emission of an optimum emitted power from a laser source to an optical disk based on the measured value obtained and the compensation data. As a result, elimination of effects of fluctuation in effective power due to objective lens shift is permitted, and it is possible to ensure that the effective power of a laser irradiating the active layer will always be maintained at an optimum laser power.