The optical disk device includes a generation means and a LC servo means. The generation means generates a lens error signal based on an electrical signal output from a pickup head. After amplifying the lens error signal with a predetermined gain, the generation means outputs the lens error signal. The LC servo means performs lens center servo control based on the lens error signal. The optical disk device further includes a measurement means which measures, before the lens center servo control, a first and a second amplitude values of the lens error signal. The measurement means calculates a current gain based on the first and second amplitude values, the latest gain which is currently set, and a predetermined target amplitude value. Then the measurement means sets the current gain to the generation means.