Electric power consumed by a laser diode when an optical disk or magneto-optical
disk is played back is reduced. A laser diode control circuit (6) causes
the laser diode to emit continuously rather than intermittently, even if a PCK
signal is supplied to the laser diode control circuit (6), when an optical
display player or magneto-optical disk drive does not yet stabilize and is being
pulled into a phase-locked state. When the focus is locked, the player is in a
phase-locked state, and the operation is stable, a mode-switching circuit (9)
included in the laser diode control circuit (6) switches the mode of operation
from continuous operation to intermittent operation according to an FLOCK signal.
The frequency of the PCK is multiplied by a frequency multiplier circuit (7),
and the pulse width is adjusted by a pulse width-adjusting circuit (8).
A laser diode driver circuit (10) produces intermittent current of this
adjusted pulse width. The laser diode is started to emit intermittently.