A three-phase power converter that comprises three single-phase power converters (1, 1u, 1v, 1w) for three phases, each single-phase power converter (1, 1u, 1v, 1w) comprising: unit cells (11-1,..., 11-M) that each includes: two semiconductor switches that are connected in series; a direct current capacitor that is connected in parallel with the two semiconductor switches; and input and output terminals (T1, T2) of a current that is discharged from the DC capacitor or charged in the DC capacitor in response to switching operation of the semiconductor switches; first and second arms (12-P, 12-N) that are each configured by one of the unit cells (11-1,..., 11-M) or a plurality of the unit cells (11-1,..., 11-M) that are cascade-connected to one another through the input and output terminals (T1, T2), the first and second arms (12-P, 12-N) comprising a same number of the unit cells (11-1,..., 11-M); an arm coupling unit that includes: a first terminal (a) to which an end of the first arm (12-P) is connected; a second terminal (b) to which an end of the second arm (12-N) is connected; a third terminal (c) to which an end of a DC power supply (V dc) is connected; and a transformer (14, 14') that includes alternating current input and output terminals (T1-1, T2-1) on a primary side and an intermediate terminal (T2-3) on a secondary side winding, wherein two end terminals (T2-1, T2-2) of the secondary side winding are connected respectively to a terminal of an end of the first arm (12-P) to which terminal the first terminal (a) is not connected and a terminal of an end of the second arm (12-N) to which terminal the second terminal (b) is not connected, and the intermediate terminal is connected to a terminal of an end of the DC power supply (V dc) to which terminal the third terminal (c) is not connected, and characterized in that the transformer (14, 14') in each of the single-phase power converter (1, 1u, 1v, 1w) configures each phase of a three-phase transformer (14, 14') that includes a star connection on a primary side and an open star connection on a secondary side, and each of the single-phase power converter (1, 1u, 1v, 1w) is commonly connected to the DC power supply (V dc). unit cells (11-1,..., 11-M) that each includes: two semiconductor switches that are connected in series; a direct current capacitor that is connected in parallel with the two semiconductor switches; and input and output terminals (T1, T2) of a current that is discharged from the DC capacitor or charged in the DC capacitor in response to switching operation of the semiconductor switches; two semiconductor switches that are connected in series; a direct current capacitor that is connected in parallel with the two semiconductor switches; and input and output terminals (T1, T2) of a current that is discharged from the DC capacitor or charged in the DC capacitor in response to switching operation of the semiconductor switches; first and second arms (12-P, 12-N) that are each configured by one of the unit cells (11-1,..., 11-M) or a plurality of the unit cells (11-1,..., 11-M) that are cascade-connected to one another through the input and output terminals (T1, T2), the first and second arms (12-P, 12-N) comprising a same number of the unit cells (11-1,..., 11-M); an arm coupling unit that includes: a first terminal (a) to which an end of the first arm (12-P) is connected; a second terminal (b) to which an end of the second arm (12-N) is connected; a third terminal (c) to which an end of a DC power supply (V dc) is connected; and a transformer (14, 14') that includes alternating current input and output terminals (T1-1, T2-1) on a primary side and an intermediate terminal (T2-3) on a secondary side winding, wherein two end terminals (T2-1, T2-2) of the secondary side winding are connected respectively to a terminal of an end of the first arm (12-P) to which terminal the first terminal (a) is not connected and a terminal of an end of the second arm (12-N) to which terminal the second terminal (b) is not connected, and the intermediate terminal is connected to a terminal of an end of the DC power supply (V dc) to which terminal the third terminal (c) is not connected, and characterized in that a first terminal (a) to which an end of the first arm (12-P) is connected; a second terminal (b) to which an end of the second arm (12-N) is connected; a third terminal (c) to which an end of a DC power supply (V dc) is connected; and a transformer (14, 14') that includes alternating current input and output terminals (T1-1, T2-1) on a primary side and an intermediate terminal (T2-3) on a secondary side winding, wherein two end terminals (T2-1, T2-2) of the secondary side winding are connected respectively to a terminal of an end of the first arm (12-P) to which terminal the first terminal (a) is not connected and a terminal of an end of the second arm (12-N) to which terminal the second terminal (b) is not connected, and the intermediate terminal is connected to a terminal of an end of the DC power supply (V dc) to which terminal the third terminal (c) is not connected, and characterized in that the transformer (14, 14') in each of the single-phase power converter (1, 1u, 1v, 1w) configures each phase of a three-phase transformer (14, 14') that includes a star connection on a primary side and an open star connection on a secondary side, and each of the single-phase power converter (1, 1u, 1v, 1w) is commonly connected to the DC power supply (V dc).