There is provided a power conversion device such that it is possible to supply a constant voltage to a load even when the voltage of a 3-phase alternating current power supply fluctuates. A series circuit formed of a switching element Q1 and switching element Q2 and a series circuit formed of a switching element Q3 and switching element Q4 are connected to both ends of a direct current power supply series circuit 3 formed of a direct current power supply Psp and a direct current power supply Psn, a bidirectional switch element S1 is connected between an alternating current output terminal U and a terminal R, a bidirectional switch element S2 is connected between the alternating current output terminal U and a neutral terminal O, a bidirectional switch element S3 is connected between an alternating current output terminal W and the neutral terminal O, a bidirectional switch element S4 is connected between the alternating current output terminal W and a terminal T, and furthermore, an alternating current output terminal V and terminal S are connected.