In a connection check mode, a camera main body sends an electromagnetic wave signal to a lens unit to enable radio communication between the camera main body and the lens unit. Then the camera main body sends its own specification data to the lens unit through the radio communication, and the lens unit judges based on the specification data as to whether the lens unit is compatible with the camera main body or not. If the answer is yes, the lens unit derives from the specification data of the camera main body data on performances of the lens unit achievable in connection to the camera main body. The judgment and the performance data are sent through the radio communication to the camera main body, and are displayed as connection data on an LCD of the camera main body.