PURPOSE: To completely close a door by regulating oil pressure applied to a piston and a rod arranged in a cylinder, to buffer the retreat speed of the door, and then increasing oil pressure to increase the retreat speed of the door.

CONSTITUTION: When letting go an opened door, oil between the socket 17 side in a cylinder 1 and a piston 13 flows through a lateral hole 14 on the piston 13 side from a small hole 12 of a check valve 11 to buffer the retreat speed of the door. When a bottle-like piece 7 connected to a rod 2 enters a hole of a valve 18, the flow resistance of oil is increased to buffer the retreat speed of the door. Further when the rear small-diameter part of the piece 7 reaches a recess cut all around a peripheral wall on one side in the hole of the valve 18, oil flow is increased, and the retreating force of the rod 2 is increased to close the door in the speed increased state.