Push-pull signal is created on the basis of reflected-light detection signals
output from four divided light receiving elements that receive a reflection of
a recording laser light beam off an optical disk. The push-pull signal is sent
to a gain variation circuit. The push-pull signal is normalized by setting the
gain of the gain variation circuit to a low level in response to a mark forming
section of a recording signal, but to a high level in response to a blank forming
section of the recording signal. Wobble detection and pre-pit detection are performed
on the basis of the normalized push-pull signal.
