In case of driving each of light emitting parts of a surface emitting
laser, each of light emitting parts is made to be in forward-bias state
and switches appropriately change bias voltage, which is lower than laser
oscillation threshold voltage, and drive voltages, which are not less
than the laser oscillation threshold voltage to directly apply the
changed voltage to each of drive ends of the light emitting parts.
Whereby, each of light emitting parts is driven.