To satisfy both of traveling stability and riding comfortableness by fixing one end of a leaf spring to a car body side, movably supporting the other end in the longitudinal direction by a bracket attached to the car body side, and slidably moving a sliding sheet on the top face of the leaf spring in the bracket.

A sliding sheet 18 is arranged in such a state as sliding on the top face in the rear end side of a leaf spring in a bracket 8 which supports the rear end of a leaf spring 2 arranged in the front/rear direction of a car body in such a state as being moved longitudinally. The sliding sheet is threadly engaged with a screw rod 14 rotatably mounted between flanges 15, 16 in the front/rear of the bracket 8 and moved in the front/rear by the rotating operation. The holding part 17 of the screw rod 14 is rotationally operated so as to move the sliding sheet 18 in the front/rear, and the effective length of the leaf spring is so adjusted that, when load is heavy, the length is shortened so as to improve the traveling stability, and when it is light, it is lengthened so as to improve riding comfortableness.