a first rail comprising a blocking feature and being formed with a predetermined space wherein the first rail comprises a first wall, a second wall and a longitudinal wall connected between the first wall and the second wall of the first rail, the predetermined space is provided by an opening formed on the longitudinal wall of the first rail, and the predetermined space is transversely communicated with a first side and a second side of the longitudinal wall of the first rail, the first side is opposite to the second side;

a second rail longitudinally movable relative to the first rail;

a slide assisting device movably mounted between the first rail and the second rail;

an elastic member arranged on the slide assisting device; and

a working member arranged on the second rail;

wherein while the second rail is moved relative to the first rail along an opening direction, the working member is configured to contact the elastic member in an initial state in order to drive the slide assisting device to move along the opening direction to a predetermined position;

wherein when the slide assisting device is located at the predetermined position, the elastic member is configured to be transversely extended into the predetermined space provided by the opening formed on the longitudinal wall of the first rail in order to release an elastic force through the predetermined space of the first rail to be switched from the initial state to a non-initial state, such that the working member no longer contacts the elastic member in the non-initial state;

wherein when the second rail is further moved relative to the first rail along the opening direction to an extension position, the blocking feature of the first rail is configured to block the working member in order to prevent the second rail from being moved from the extension position along the opening direction.