A power conversion apparatus comprising: a three-phase transformer interconnected to a three-phase power system; said three-phase transformer including: a primary winding group configured to receive three-phase electric power of said three-phase electric power system; a first secondary winding group and a second secondary winding group configured to receive electric power transferred from said primary winding group; a first converter group and a second converter group connected to said first and second secondary winding groups (201A, 201B), respectively; a positive-side DC output terminal; and a negative-side DC output terminal, said primary winding group having first to third primary windings (205 to 207), said first secondary winding group having first to third secondary windings (208A to 210A) having respective one ends star-connected at a neutral point, said second secondary winding group having fourth to sixth secondary windings (208B to 210B) having respective one ends star-connected at a neutral point, the respective neutral points of said first and second secondary winding groups (201A, 201B) being connected to each other, said first converter group having first to third converter arms (113 to 115) having respective one ends connected to other ends of said first to third secondary windings (208A to 210A), and said second converter group having fourth to sixth converter arms (117 to 119) having respective one ends connected to other ends of said fourth to sixth secondary windings (208B to 210B), the other ends of said first to third converter arms (113 to 115) are all connected to said positive-side DC output terminal, and the other ends of said fourth to sixth converter arms (117 to 119) are all connected to said negative-side DC output terminal. a three-phase transformer interconnected to a three-phase power system; said three-phase transformer including: a primary winding group configured to receive three-phase electric power of said three-phase electric power system; a first secondary winding group and a second secondary winding group configured to receive electric power transferred from said primary winding group; a first converter group and a second converter group connected to said first and second secondary winding groups (201A, 201B), respectively; a positive-side DC output terminal; and a negative-side DC output terminal, a primary winding group configured to receive three-phase electric power of said three-phase electric power system; a first secondary winding group and a second secondary winding group configured to receive electric power transferred from said primary winding group; a first converter group and a second converter group connected to said first and second secondary winding groups (201A, 201B), respectively; a positive-side DC output terminal; and a negative-side DC output terminal, said primary winding group having first to third primary windings (205 to 207), said first secondary winding group having first to third secondary windings (208A to 210A) having respective one ends star-connected at a neutral point, said second secondary winding group having fourth to sixth secondary windings (208B to 210B) having respective one ends star-connected at a neutral point, the respective neutral points of said first and second secondary winding groups (201A, 201B) being connected to each other, said first converter group having first to third converter arms (113 to 115) having respective one ends connected to other ends of said first to third secondary windings (208A to 210A), and said second converter group having fourth to sixth converter arms (117 to 119) having respective one ends connected to other ends of said fourth to sixth secondary windings (208B to 210B),