A Schottky barrier diode 44 is formed between a P-gate diffusion region 33 and an N-type silicon substrate 31 in a photothyristor on a CH1 side and a photothyristor on a CH2 side. With this arrangement, the injection of minority carriers from the P-gate diffusion region 33 to the N-type silicon substrate 31 is restrained to reduce the amount of remaining carriers, and an excessive amount of carriers remaining in the N-type silicon substrate 31 during commutation has a reduced chance of moving toward the opposite channel side, allowing the commutation characteristic to be improved. Therefore, by a combination with an LED, there can be provided a light-fired coupler for firing and controlling the load.