A camera system operable with data carried from a camera accessory to a camera body. The camera accessory has a ROM for storing various data at a plurality of addresses, respectively, each of which data consists of a plurality of bits, and a coupling terminal for receiving a train of clock pulses from the camera body. A circuit is also provided for sequentially designating the address of the ROM one by one to permit by ROM to output a data stored at the designated address. In the circuit, an address signal is formed in response to the clock pulses, received through the coupling terminal, for designating an address. The data derived from the ROM are transmitted to the camera body.