A slide cover has a engaged portion formed thereon. A rotatable member includes a stopper portion which is abutted against the engaged portion so as to restrict a relative movement of the engaged portion of the slide cover when the slide cover is arranged at a closed position. The stopper portion is positioned away from a rotation center of the rotatable member, and the rotatable member rotates to allow the relative movement of the engaged portion when the stopper portion is pushed by the engaged portion. This makes it possible to increase an angle between an stopper surface formed on the stopper portion and a movement direction (right-left direction) of the engaged portion. As a result, the cover is stably held at the closed position.