Accessory, interchangeable lens and camera body

An accessory that is mountable at a camera body and includes a plurality of terminals via which communication is carried out with the camera body, comprising:

• a first terminal through which a first clock signal is output to the camera body;
• a second terminal through which information pertaining to a drive target member that is driven by a drive unit is output to the camera body in synchronization with the first clock signal;
• a third terminal through which a second clock signal is input from the camera body;
• a fourth terminal through which a first value is transmitted to the camera body in synchronization with the second clock signal, the first value indicating a communication specification according to which the information is transmitted through the second terminal to the camera body;
• a fifth terminal through which a second value is received from the camera body in synchronization with the second clock signal after the first value is transmitted through the fourth terminal, the second value indicating a communication specification according to which the information is transmitted through the second terminal to the camera body;
• a sixth terminal used to indicate whether or not communication with the camera body is enabled;
• a seventh terminal through which a second source voltage from the camera body is supplied;
• an eighth terminal used as a ground potential for the second source voltage;
• a ninth terminal through which a first source voltage from the camera body is supplied;
• a tenth terminal used as a ground potential for the first source voltage;
• an eleventh terminal used for the camera body to detect that the accessory is mounted;
• and
• a control unit that starts transmission of the information through the second terminal according to the communication specification indicated by the second value upon receiving the second value through the fifth terminal.