PURPOSE: To improve stability and a riding sensation by varying roll rigidity of a car body through simple constitution and changing the roll rigidity according to the running state and the operating state of a vehicle.

CONSTITUTION: A plate-form spring member 23 having a base end is supported on the car body side rotatably around an axis and a spring constant differed with a direction in which a load exerted on the tip thereof is exerted around the axis, and a displacement transmitting means 26 to transmit displacement of a suspension arm 13 to the tip of the spring member 23 are provided. An operating state, such as a steering angle and a car speed, is detected by a detecting means and the plate-form spring member 23 is rotated around the axis through the working of an electric motor 29 according to the given operating state.