A power conversion device comprising: a power converter including an arm configured with a plurality of unit converters connected in series; and a control device configured to control the power converter, each of the plurality of unit converters (10A, 10B) including a main circuit including a switching element (Q1 to Q4) and a DC capacitor and configured to output a voltage pulse according to voltage of the DC capacitor by turning on/off of the switching element (Q1 to Q4), a control circuit configured to control on/off of the switching element (Q1 to Q4) in accordance with a control signal received from the control device, and a power supply configured to lower voltage of the DC capacitor to generate power supply voltage to be supplied to the control circuit, the power supply including a power supply circuit configured to convert input voltage provided between first and second input terminals (54A, 54B) from the DC capacitor into the power supply voltage, a thyristor connected between the first and second input terminals (54A, 54B) electrically in parallel with the power supply circuit, and a reverse current blocking diode connected between an anode and a cathode of the thyristor electrically in series with the power supply circuit to prevent reverse flow of current from the power supply circuit to the thyristor; characterized in that the power supply further includes a current-limiting resistor connected between terminals of the DC capacitor electrically in series with the thyristor, and a control unit configured to fire the thyristor when the input voltage applied to the power supply circuit exceeds a threshold voltage (DCOV),. wherein when the input voltage applied to the power supply circuit exceeds the threshold voltage (DCOV), the control circuit receives supply of power supply voltage from the power supply to transmit a signal indicating abnormality of the unit converter (10A, 10B) to the control device, and the control device is configured to transmit the control signal for fixing the switching element (Q1 to Q4) to an off state to the control circuit of each of the unit converters (10A, 10B), when receiving a signal indicating abnormality of the unit converter (10A, 10B) from the control circuit of any one of the plurality of unit converters. a power converter including an arm configured with a plurality of unit converters connected in series; and a control device configured to control the power converter, each of the plurality of unit converters (10A, 10B) including a main circuit including a switching element (Q1 to Q4) and a DC capacitor and configured to output a voltage pulse according to voltage of the DC capacitor by turning on/off of the switching element (Q1 to Q4), a control circuit configured to control on/off of the switching element (Q1 to Q4) in accordance with a control signal received from the control device, and a power supply configured to lower voltage of the DC capacitor to generate power supply voltage to be supplied to the control circuit, the power supply including a power supply circuit configured to convert input voltage provided between first and second input terminals (54A, 54B) from the DC capacitor into the power supply voltage, a thyristor connected between the first and second input terminals (54A, 54B) electrically in parallel with the power supply circuit, and a reverse current blocking diode connected between an anode and a cathode of the thyristor electrically in series with the power supply circuit to prevent reverse flow of current from the power supply circuit to the thyristor; characterized in that the power supply further includes a current-limiting resistor connected between terminals of the DC capacitor electrically in series with the thyristor, and a control unit configured to fire the thyristor when the input voltage applied to the power supply circuit exceeds a threshold voltage (DCOV),. wherein when the input voltage applied to the power supply circuit exceeds the threshold voltage (DCOV), the control circuit receives supply of power supply voltage from the power supply to transmit a signal indicating abnormality of the unit converter (10A, 10B) to the control device, and the control device is configured to transmit the control signal for fixing the switching element (Q1 to Q4) to an off state to the control circuit of each of the unit converters (10A, 10B), when receiving a signal indicating abnormality of the unit converter (10A, 10B) from the control circuit of any one of the plurality of unit converters.