Upon turn-off of IGBT, by suppressing variations in collector-emitter voltage between IGBTs connected in series, risk of breaking IGBT due to overvoltage breakdown can be reduced. In protection circuit provided for each of the plurality of IGBTs 50 connected in series, between collector and emitter of IGBT 50, avalanche elements D1˜D5, resistance R4 and avalanche element D6 are sequentially connected in series. Capacitor C1 and resistance R1 are connected parallel between both ends of the avalanche element D4, and capacitor C2 and resistance R2 are connected parallel between both ends of the avalanche element D5. Between a common connection point of the resistance R4 and the avalanche element D6 and gate of the IGBT 50, resistance R5, a parallel circuit of capacitor C3 and resistance R6, and a series component of Zener diodes ZD1 and ZD2 whose polarities are opposite to each other, are connected in series.