A power conversion portion (10) and a connection portion (20) converting power between a fuel cell (FC) and a battery (BAT) corresponding to dc power supply and a motor generator (MG) corresponding to an ac machine, are configured of a matrix converter. For a power flow pattern requiring that the dc power supply provide high voltage, a switch (SCd) in the connection portion (20) operates in response to a control signal received from a control device (30) to electrically connect a power supply line (LC) to a power supply line (Ld) to connect the fuel cell (FC) and the battery (BAT) in series.