To facilitate changing or adjusting a detecting timing and a detecting position of a detector and to reduce the types of detectors to be held.

There are provided a switch body 19A for detecting whether or not a mechanical displacement of a cover 14 exceeds a preliminarily set detection threshold value when the mechanical displacement is detected, an arm 19B for detection which is interposed between the switch body 19A and a projection 17 for detection of the cover 14 to transmit the mechanical displacement of the projection 17, and an elastic member 19C which is integrally set with the arm 19B to change a relative value of the mechanical displacement with respect to the detection threshold value in accordance with a flexural rigidity and transmits the mechanical displacement to the arm 19B.