PURPOSE: To restrain the short-circuit current of a gate driving device, by outputting a signal to a control unit to restrain an AC output when the output current of a DC power source has exceeded a predetermined value.

CONSTITUTION: The gate driving device 2' of a GTO (self arc-extinguishing switching) element 1 is provided with an opening and closing control unit 23' and a current detecting unit 27, detecting the output current of a DC power source 3. The current detecting unit 27 decides whether the output current of the DC power source 3 has exceeded a predetermined value or not and outputs a signal to the opening and closing control unit 23' when it has exceeded the predetermined value. When the GTO 1 is broken down and short-circuit is generated between a gate and a cathode, for example, a large short-circuit current is conducted through the secondary side of a transformer 21. The short- circuit current is detected by the current detecting unit 27 and a commanding signal for preventing overcurrent is outputted while the commanding signal is inputted into the opening and closing control unit 23' and a modulating circuit reduces the pulse width of an output pulse extremely.