A converter section (2) includes three pairs of switching elements (Srp, . . . , Stn), each pair having two switching elements connected in series between two direct current links (L1, L2), and phases of an input three-phase alternating current are connected to nodes between the series-connected switching elements one by one. Each of the switching elements (Srp, . . . , Stn) is made of a transistor having a bipolar structure. The control unit (5) controls the switching elements (Srp, . . . , Stn) such that line voltages between a reference phase, which is one of the phases of the input three-phase alternating current, and each of the other phases are output to the two direct current links (L1, L2) on a time division basis. The control unit (5) applies a predetermined gate voltage to one or more of the switching elements (Srp, . . . , Stn) to which a reverse bias is applied.