PURPOSE: To exhibits the same cushioning function even if any person having respective body weight takes a seat by adjusting the spring property of springs.

CONSTITUTION: A seat body is supported in such a manner as to be freely movable vertically by providing two sets of crossing pipes 22, 23 between a seat plate 2 and the seat body 3. In addition, springs 4 and a pair of flexural coupling links 8, 9 are provided between the seat plate and t7he seat body. In a seat cushion providing a damper 19 between each coupling link, an adjustable plate 29 is rotatably provided on the upper side or the lower side of the seat plate. (A plurality of supporting faces having different height are formed on the adjustable plate. The results selectively support supporting members 33 provided below the springs on one of the supporting faces with the rotation of the adjustable plate.