A power conversion device including a plurality of DC/DC converters (10, 10a-10e), primary side terminals (1a, 1b) of which are connected in parallel and secondary side terminals (2a, 2b) of which are connected in series, the DC/DC converters (10, 10a-10e) each comprising: - a transformer (3, 3a); - a first switching circuit (4, 4a) formed of a bridge circuit including a plurality of legs having a plurality of semiconductor switching elements (Q11-Q16) to which antiparallel diodes (D11-D16) are respectively connected, the first switching circuit (4, 4a) being connected between the primary side terminals (1a, 1b) and a primary winding of the transformer (3, 3a) so as to perform DC/AC power conversion; - a second switching circuit (5, 5a) formed of a bridge circuit including a plurality of legs having a plurality of semiconductor switching elements (Q21-Q26) to which antiparallel diodes (D21-D26) are respectively connected, the second switching circuit (5, 5a) being connected between the secondary side terminals (2a, 2b) and a secondary winding of the transformer (3, 3a) so as to perform AC/DC power conversion; - a capacitor connected in parallel to the secondary side terminals (2a, 2b); and - a control circuit (20, 20a-20c) configured to control the first switching circuit (4, 4a) and the second switching circuit (5, 5a), wherein each semiconductor switching element comprises a gate drive circuit (30a, 30b) and wherein - a gate drive circuit (30a, 30b) of at least one of the semiconductor switching elements in each of the legs of the first switching circuit (4, 4a) and the second switching circuit (5, 5a), includes a malfunction detection unit for detecting a malfunction in the semiconductor switching element, - the control circuit (20, 20a-20c) is provided with a normal operation mode, a protection mode for turning OFF all the semiconductor switching elements (Q11-Q16) in the first switching circuit (4, 4a), a discharge mode for discharging the capacitor and a bypass mode for bypassing the capacitor, and - in each of the DC/DC converters (10, 10a-10e), when the malfunction detection unit detects the malfunction in the semiconductor switching element, the control circuit (20, 20a-20c) is configured to halt the normal operation mode, to control the first switching circuit (4, 4a) by the protection mode, and to control the second switching circuit (5, 5a) by the bypass mode after controlling the second switching circuit (5, 5a) by the discharge mode, wherein in the discharge mode, the control circuit (20, 20a) is configured to discharge the capacitor by turning ON the semiconductor switching elements (Q21-Q26) in a predetermined leg in the second switching circuit (5, 5a), such that the predetermined leg malfunctions after being used for discharge, and wherein in the bypass mode after the discharge mode, the control circuit (20, 20a) is configured to cause a short circuit between the secondary side terminals (2a, 2b) to bypass the capacitor by turning ON all the semiconductor switching elements, in the second switching circuit (5, 5a) in a leg separate from the predetermined leg used in the discharge mode which is a sound leg that does not include the semiconductor switching element where the malfunction has been detected. - a transformer (3, 3a); - a first switching circuit (4, 4a) formed of a bridge circuit including a plurality of legs having a plurality of semiconductor switching elements (Q11-Q16) to which antiparallel diodes (D11-D16) are respectively connected, the first switching circuit (4, 4a) being connected between the primary side terminals (1a, 1b) and a primary winding of the transformer (3, 3a) so as to perform DC/AC power conversion; - a second switching circuit (5, 5a) formed of a bridge circuit including a plurality of legs having a plurality of semiconductor switching elements (Q21-Q26) to which antiparallel diodes (D21-D26) are respectively connected, the second switching circuit (5, 5a) being connected between the secondary side terminals (2a, 2b) and a secondary winding of the transformer (3, 3a) so as to perform AC/DC power conversion; - a capacitor connected in parallel to the secondary side terminals (2a, 2b); and - a control circuit (20, 20a-20c) configured to control the first switching circuit (4, 4a) and the second switching circuit (5, 5a), - a gate drive circuit (30a, 30b) of at least one of the semiconductor switching elements in each of the legs of the first switching circuit (4, 4a) and the second switching circuit (5, 5a), includes a malfunction detection unit for detecting a malfunction in the semiconductor switching element, - the control circuit (20, 20a-20c) is provided with a normal operation mode, a protection mode for turning OFF all the semiconductor switching elements (Q11-Q16) in the first switching circuit (4, 4a), a discharge mode for discharging the capacitor and a bypass mode for bypassing the capacitor, and - in each of the DC/DC converters (10, 10a-10e), when the malfunction detection unit detects the malfunction in the semiconductor switching element, the control circuit (20, 20a-20c) is configured to halt the normal operation mode, to control the first switching circuit (4, 4a) by the protection mode, and to control the second switching circuit (5, 5a) by the bypass mode after controlling the second switching circuit (5, 5a) by the discharge mode, wherein in the discharge mode, the control circuit (20, 20a) is configured to discharge the capacitor by turning ON the semiconductor switching elements (Q21-Q26) in a predetermined leg in the second switching circuit (5, 5a), such that the predetermined leg malfunctions after being used for discharge, and