To provide a non-rail type gate capable of opening by a light force and gently closing automatically or by application of a slight starting force.

A housing 1 is provided with a closing mechanism constructed of a door closer 39 always applying a force in the closing direction. In addition to the closing mechanism, closing force reducing mechanisms 43, 44, 45, 50 and 51 converting lowering force by gravity of themselves into an opening directional force to the sliding door and applying the opening directional force to the sliding door are arranged in the housing. In each of the closing force reducing mechanisms, one end part is pivoted to the rear end upper part of the housing, while the other end part is pivoted to the door end part of the sliding door. The closing directional force f1 by the closing mechanism is set to be slightly greater than the opening force f2 plus f3 by the closing force reducing mechanisms.