POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To easily connect an external power supply when the power supply capacity to be used increases. SOLUTION: An operation is performed by power supplied by a power supply and at least three terminals a, b and c are provided in an equipment. The equipment side of the terminal a is connected to an internal power supply provided inside the equipment, the equipment side of the terminal b is connected to a power supply voltage line for operating the equipment and the equipment side of the terminal c is provided with an external connection means connected to a ground line. The external connection means attains a connectable state by selecting a first connection means provided with at least two terminals a and b for which the terminal a and the terminal b are short-circuited or a second connection means provided with at least two terminals b and c for which the external power supply is connected between the terminal b and the terminal c.