The invention provides an adapter, a camera system and an adapter control program. The adapter has a first interface part which can be used to mount and dismount a camera body, a second interface part which is separately from the first interface part and can be used to mount and dismount an interchangeable lens, and a power supply part which generates a power supply voltage of a third power supply and a fourth power supply system that supply the interchangeable lens mounted on the second interface part through a first power supply system and a second power supply system in a second power supply system of the camera body mounted on the first interface part, wherein the second power supply system is different from the first power supply system.