Abstract: A case has an engagement hole formed in a side surface thereof in the width direction, a cover has a projecting piece formed thereon, the projecting piece projecting toward the case side, and a tip portion of the projecting piece is fitted into the engagement hole from the inside. A reset bar has a recessed portion formed in a preset range extending in the depth direction and the circumferential direction within the outer peripheral surface of the reset bar and, when positioned at either an initial position or an automatic reset position, prevents the tip portion from being pushed inside by having the outer peripheral surface opposed to the back side of the projecting piece. In addition, when positioned at a manual reset position, the reset bar allows the tip portion to be pushed inside by having the recessed portion opposed to the back side of the projecting piece.