In an uninterruptible power supply apparatus, a common mode current flowing from nodes (N1 to N3) to a line of a ground voltage (GND) through a stray capacitance (41) of a battery (40) is limited by a common mode reactor (34), and the low-level common mode current passing through the common mode reactor (34) is caused to flow to a virtual neutral line (NL) through a common mode capacitor (37). Therefore, the level of noise caused by the common mode current can be reduced.