PURPOSE: To reduce to a half the number of times of charging and discharging of a stray capacity of an insulated gate in view of alleviating a gate power by continuously applying an insulated gate signal to an insulated gate electrode for turning on from the turning off period to the turning on period.

CONSTITUTION: The gate control signal SGON(1') and SGOF are respectively applied, through amplifiers 22 and 23, to an insulated gate electrode GON for turning on and an insulated gate electrode GOFF for turning off of a thyristor 21 with insulated gate. Thereby, a logic circuit 25 converts the gate control signal SGOF to the signal which is delayed by the predetermined period (t1) from the falling edge of the gate control signal SG Moreover, a logic circuit 41 converts the gate control signal SGON(1) to the signal which rises synchronously with the rise of the gate control signal SG and falls after the predetermined period (Δt11) from the fall of the gate control signal SG. Thereby, the number of pulses to be applied to the insulated gate GON for turning on can be reduced to a half.