A printer is disclosed which determines whether or not an opening of the printer is open or closed. The printer includes an opening/closing mechanism for opening and closing the opening of the printer housing. The printer includes a controller configured to determine whether the opening is open or closed based on a light receiving state of a light receiving portion. The light receiving portion receives light from a light sending portion. A first movable body with a plurality of openings is moveable between the light sending and receiving portions. A movement transmission mechanism moves the first moveable body according to movement of a second moveable body.