In a device combination system of the present invention, END setting parameters are read from a main body. A power supply converter and END setting parameters are obtained from a camera head and a battery. An END setting value is set according to these END parameters. A CPU determines whether or not the battery being mounted is in an unusable state that it is exhausted to a dead level. With the above arrangement, there is provided a device combination system in which a battery check function provided in a power supply device works normally regardless of a type of a device mounted on the power supply device.