PURPOSE: To improve cut-off capacity of a GTO by bringing OFF source voltage higher than the breakdown voltage of gate and producing OFF current with voltage higher than the breakdown voltage during accumulation time then applying capacitor voltage onto the gate after accumulation time thereby increasing dig/dt.

CONSTITUTION: When a monostable operation circuit 12 produces an output at time (t1) based on a command fed from a logic section 2 and a switch 6 is turned ON under ON state of a GTO3, gate current (ig) flows through a capacitor 11, the switch 6 and the cathode and gate of the GTO3 to bring out a state where gate current flows easily because the OFF source 10 voltage is higher than the breakdown voltage of the gate thus providing a high dig/dt. Upon elapse of time T, output from the monostable operating circuit 12 disappears at time (t3) and the switch 6 is turned OFF. When the source 10 voltage is E and the resistances of resistors 13-15 are R1, R2, R3, a weak reverse voltage E.R1/(R1+R2+R3) is applied and the OFF state is maintained.