A white dot out detecting device according to the present invention comprises a recording/reproduction control signal generator for generating a recording/reproduction control signal showing a recording state or a reproducing state of an optical disk, a variable gain amplifier for amplifying and outputting an information signal read from the optical disk and adjusting a gain in the amplification based on the recording/reproduction control signal, an envelope detector for detecting an output envelope of the variable gain amplifier, an integrator for integrating an output of the envelope detector, a slice level setting unit for setting a slice level as a reference for detecting a white dot out based on an output of the integrator, a comparator for detecting the white dot out based on comparison of the output of the envelope detector and the slice level to each other, and a level shifter for temporarily shifting the slice level to a high-level side when a change of the recording/reproduction control signal is detected.