Abstract: A hydropneumatic suspension for a left wheel and a hydropneumatic suspension assembly for a right wheel are connected to each other by means of an anti-roll cylinder. A sub-tank is connected to each suspension assembly. A spring constant switching valve is disposed between each suspension assembly and its corresponding sub-tank. The sub-tanks are charged with a compressed inert gas. When a vehicle turns, the anti-roll cylinder operates so that some of oil is discharged from the inside suspension assembly, while oil is supplied to the outside suspension assembly. While the vehicle is turning, the spring constant switching valve for outside suspension assembly is opened, so that the outside suspension assembly is caused to communicated with its corresponding sub-tank, whereby the spring constant of the outside suspension assembly is lowered. When the turning movement is finished, the spring constant switching valve is closed, so that the suspension assembly is disconnected from the sub-tank.