Abstract: Disclosed is an attachment member including a substantially circular body adapted to be releasably attachable to the outer periphery of an exchangeable lens of the type, which when mounted on a single lens reflex camera body, is adapted to transmit to the camera body only information as to the step-difference between a minimum f-number of the lens and a f-number set by a diaphragm setting ring of the lens. The attachment member includes a transmitting member on the substantially circular body at an angular position dependent upon the maximum f-number of the exchangeable lens to be used therewith. Thus when the attachment member is attached to an exchangeable lens at the predetermined angular position, the attachment member is capable of transmitting to a camera body information as to the maximum f-number of the exchangeable lens.