A biasing member 214 is configured to provide a pressing member 113 with biasing force acting to bias the pressing member 113 against a detecting portion 111 before the pressing member 113 receives reaction force from the detecting portion 111 when an opening/closing member 101 is closed. The support portion 113a receives reaction force acting to the pressing member 113 from the detecting portion 111, while the opening/closing member 101 is closed, and the pressing member 113 maintains an operation state independently with respect to the detecting portion 111, while the opening/closing member 101 is closed.