A lock mechanism is provided with a lock member moved between a locking position for locking a first apparatus and a second apparatus, and a non-locking position for not locking the first apparatus and the second apparatus, and a restraining portion for restraining the lock member in the non-locking position. With an operation of bringing the second apparatus and the first apparatus close to each other from a state in which the first apparatus and the second apparatus are spaced apart from each other, the restraint of the lock member by the restraining portion is released, and the lock member is moved from the non-locking position to the locking position.