A power supply device includes: a first line, a second line, and a third line, each having a different electric potential from one another; a battery circuit in which a fuel cell stack and an electric storage device are connected in series; and a first DC-DC converter, wherein 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 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.