NOVELTY - A power supply device (10) comprises a first line (L1), a second line (L2), and a third line (L3), each having a different electric potential from one another; a battery circuit (10a) in which a fuel cell stack (11) and an electric storage device are connected in series; and a first direct current (DC)-DC converter.    USE - The power supply device is useful for producing power supply system of fuel cell vehicle (claimed).    ADVANTAGE - Using the device above, compared to the case where DC-DC converter is equipped individually to each of the fuel cell stack and the electric storage device, the cost required for configuration can be lowered, and the size can be made smaller. It is possible to prevent a decline in inductance compared to the case where choke coils are simply connected in parallel.    DETAILED DESCRIPTION - A power supply device (10) comprises a first line (L1), a second line (L2), and a third line (L3), each having a different electric potential from one another; a battery circuit (10a) in which a fuel cell stack (11) and an electric storage device are connected in series; and a first direct current (DC)-DC converter, where both ends of the battery circuit are connected to the first line and the third line, a connection point of the electric storage device and the fuel cell stack of the battery circuit is connected to the second line, a primary side of the first DC-DC converter (13) is connected to the second line and the third line, a secondary side of the first DC-DC converter is connected to the first line and the third line, and electric power is outputted from the first line and the third line. An INDEPENDENT CLAIM is a power supply system of a fuel cell vehicle comprising the power supply device; and an electric motor that drives a vehicle, the electric motor being supplied with electric power from the power supply device.    DESCRIPTION OF DRAWING(S) - The drawing shows a configuration diagram of power supply device.    Power supply device (10)    Battery circuit (10a)    Fuel cell stack (11)    Battery (12)    First DC-DC converter (13)    Air pump inverter (14)    Drive motor inverter (15)    Bridge circuit (31)    Choke coil (32)    Smoothing capacitor (33)    First line (L1)    Second line (L2)    Third line (L3)