Abstract: The bias current of a current injection-type light-emitting element is set very close to the threshold current, and to guarantee a stable optical output and high-speed initiation of the light-emitting operation. In the bias current supply circuit 12, particularly in closed-loop circuit 20, feedback operation of bias APC with variable bias current Ib is performed so that monitor voltage VM1 comes to equal reference voltage VA1. With this feedback operation, the steady state of VM1=VA1 is reached, and drive current Ib (Iba+Ibb) sent to laser diode 10 converges to a constant value. After a prescribed time, S/H circuit 34 is switched to hold mode. As a result, drive current Ib (Iba+Ibb) is temporarily held to a constant value corresponding to the prescribed optical output.