A sliding device includes a fixed rail, a movable rail, a lock plate, and a spring member. A seat body is fixed to the movable rail, and the movable rail is slidable relative to the fixed rail. The lock plate is held by the movable rail, and is displaceable between a locking position where the lock plate engages with the fixed rail and restricts slide of the movable rail and a non-locking position where the restriction is released. The spring member exerts an elastic force to maintain the lock plate in the locking position.