A mount lock apparatus for a camera includes a projecting exterior portion provided substantially at a central portion of a front surface of a camera body; a circular annular mount plate, which is fitted to the projecting exterior portion, and to which a photographing lens unit is detachably attached; a mount lock pin which is biased to protrude from the circular annular mount plate to engage with the photographing lens unit; and a mount unlocking button which is operated to move the mount lock pin in a direction to retract from the connecting surface. The mount unlocking button is provided on a portion of an outer peripheral surface of the projecting exterior portion that is located closer to a lens optical axis thereof than a farthermost portion of the projecting exterior portion from the lens optical axis in a horizontal direction of the camera body.