A drive device having an improved capability of reproducing data is disclosed. If an error occurs during a reproducing operation, reproduction is retried after changing amplitude reference values depending on whether the recording laser power is adequate. This makes it possible for the retrying operation to successfully read data that the previous reproducing operation failed to correctly read owing to an inadequate recording laser power. The determination as to whether the recording laser power is adequate is performed on the basis of the degree of asymmetry of the waveform of a data signal read by head means.