A cover mechanism is provided for an opening and closing device, which includes a fixed plate arranged at a first housing; a moving plate arranged at a second housing; a hinge arm that is arranged between the two plates and rotates to move the moving plate between a closed position where the first and second housings overlap and an open position where surfaces of the first and second housings are substantially coplanar; and a recess formed at the second housing that prevents the hinge arm from interfering with the second housing in the open position. The cover mechanism includes a cover arranged at the moving plate that covers the recess when the moving plate is positioned at the closed position and moves from the covering position by engaging with and being urged by the rotating hinge arm; and an urging part that urges the cover toward the covering position.