A camera having an apparatus for adjusting a back focus by varying a distance between a rearmost point of lens groups of a photographing optical system and focal plane. The apparatus includes a stationary barrel that supports the lens groups and is fixed to the camera body, and a restricting mechanism that is provided between the camera body and the stationary barrel. The restricting mechanism restricts rotational movement of the stationary barrel with respect to the camera body, while allowing movement of the stationary barrel in an optical axis direction with respect to the camera body.