In a power conversion apparatus, an AC/DC conversion circuit part converts AC power supplied from an AC input and output part into DC power. A DC/DC conversion circuit part including a transformer converts the DC power supplied from the AC/DC conversion circuit part into AC power, converts converted AC power into DC power after voltage conversion by the transformer and outputs converted DC power to a DC input and output part. A smoothing capacitor is provided in a connection part between the AC/DC conversion circuit part and the DC/DC conversion circuit part to smooth a voltage at the connection part. A connection switchover part changes a maximum value of the AC voltage at the AC input and output part by switching over a connection state between the AC input and output part and an AC device.