An electric power conversion system, comprising: a DC power supply; a plurality of main circuit switching devices (4u, 4v, 4w, 4x, 4y, 4z) bridge-connected to convert DC of the DC power supply to AC, each respectively having a freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z) connected in reverse parallel thereto; and reverse voltage application circuits (7; 7A to 7E) each respectively for applying a reverse voltage smaller than a voltage of the DC power supply to corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), upon a cutoff of back-flow current of the corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), characterized in that each of the reverse voltage application circuits (7; 7A to 7E) comprises a series connection of: a reverse voltage application switching device having a lower withstand voltage than corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and adapted to turn on upon a reverse recovery of corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), the reverse voltage application switching device being a device having holes as a majority carrier; an auxiliary diode (12; 12A) having a shorter reverse recovery time than the corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z); and a low-voltage DC power supply having a lower voltage than the DC power supply, the corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and the reverse voltage application switching device each driven by an output of the low-voltage DC power supply. a DC power supply; a plurality of main circuit switching devices (4u, 4v, 4w, 4x, 4y, 4z) bridge-connected to convert DC of the DC power supply to AC, each respectively having a freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z) connected in reverse parallel thereto; and reverse voltage application circuits (7; 7A to 7E) each respectively for applying a reverse voltage smaller than a voltage of the DC power supply to corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), upon a cutoff of back-flow current of the corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), characterized in that each of the reverse voltage application circuits (7; 7A to 7E) comprises a series connection of: a reverse voltage application switching device having a lower withstand voltage than corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and adapted to turn on upon a reverse recovery of corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), the reverse voltage application switching device being a device having holes as a majority carrier; an auxiliary diode (12; 12A) having a shorter reverse recovery time than the corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z); and a low-voltage DC power supply having a lower voltage than the DC power supply, the corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and the reverse voltage application switching device each driven by an output of the low-voltage DC power supply. a reverse voltage application switching device having a lower withstand voltage than corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and adapted to turn on upon a reverse recovery of corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z), the reverse voltage application switching device being a device having holes as a majority carrier; an auxiliary diode (12; 12A) having a shorter reverse recovery time than the corresponding freewheeling diode (5u, 5v, 5w, 5x, 5y, 5z); and a low-voltage DC power supply having a lower voltage than the DC power supply, the corresponding main circuit switching device (4u, 4v, 4w, 4x, 4y, 4z) and the reverse voltage application switching device each driven by an output of the low-voltage DC power supply.