PURPOSE: To reduce loss and size of a gate drive circuit, by employing a pulsating ON-gate current which is fed to a gate when a GTO thyristor is conducted.

CONSTITUTION: In a gate drive circuit for a GTO thyristor G, a DC power source E1, a switch S2 and a resistor R2 constitute a forward bias circuit while a power source E2 and a switch S3 constitute a reverse bias circuit. Furthermore, a series circuit of a switch S1 and a resistor R1 is arranged in parallel with a series circuit of the switch S2 and the resistor R2 so as to constitute an overdrive circuit. GTO firing/extinguishing signals are fed through a mono- stable gate M to the switch S1. An AND gate A is arranged in the way of a path for providing GTO firing/extinguishing signals to the switch S2, and an oscillator O is connected to one input thereof. Since the forward bias current is not continuous but pulsating, average loss in the circuit can be reduced.