An adapter includes: a first mount section that is detachably attached to a camera body; a second mount section that is provided separately from the first mount section and is detachably attached to any one of a plurality of types of interchangeable lenses which are different from each other in a method of controlling a diaphragm; and an accessory control section that controls the diaphragm of the interchangeable lens in response to a common control command which is received from the camera body regardless of the type of the interchangeable lens mounted on the second mount section.