In controlling an optical switch that includes an incoming light deflection section to deflect incoming light from a predetermined input port in an arbitrary direction, and an outgoing light deflection section to deflect outgoing light from the incoming light deflection section in an arbitrary direction and couple the outgoing light to a predetermined output port, a monitoring section monitors optical coupling efficiency of the outgoing light into the output port and controller controls deflection characteristics of the deflection sections so that the monitored optical coupling efficiency is maximized. Therefore, even when optimal controlled variables for the optical switch are displaced due to temperature drift and/or drift over time, the time taken to find the optimal controlled variables can be significantly reduced and rapid switching of optical paths can be achieved.