To eliminate an effect of inverse current from another power supply unit at the time of parallel operation with a simple structure.

In parallel operation, for example, when a rectifying switching element 6 of a power supply unit body 9a is ON, the inverse current from another one of power supply unit bodies 9b to 9n tries to flow via the rectifying switching element 6 of the power supply unit body 9a. However, when the inverse current is detected by a current transformer 11, a rectifying switching element stop circuit 16 turns off the rectifying switching element 6. It is thus possible to prevent the inverse current from another one of the power supply unit bodies 9b to 9n only with the current transformer 11 and the rectifying switching element stop circuit 16.