In an uninterruptible power supply apparatus, a converter (1) is controlled such that terminal-to-terminal voltage (VDC) of a capacitor (Cd) becomes a first reference voltage (VDCr1) in an inverter power feed mode and a bypass power feed mode. In a switching period in which the inverter power feed mode and the bypass power feed mode are switched, the converter is controlled such that the terminal-to-terminal voltage of the capacitor becomes a second reference voltage (VDCr2) higher than the first reference voltage to prevent circulating current (IC) from flowing through a path including the capacitor.