PURPOSE: To improve the vibration-transmission preventing performance for a chassis by automatically switching the spring characteristic of a rolling stopper to each corresponding characteristic value.

CONSTITUTION: When a large input and a large impact are applied, the coil 53 of a solenoid valve 50 is automatically excited, and a valve 52 is opened, and the second valve 55 closes an orifice 54a, and then a feeding hole 40b communicates to a communication hole 41, and the pressurized air in an accumulator 40 flows into an air spring 34 through the feeding hole 40b and the communication hole 41, and the air spring is 34 hardened and automatically switched to develop a large damping. In the state of small vibration displacement, the coil 53 is automatically set into nonexcited state, and the valve 52 closes the feeding hole 40b by the aid of a spring 51, and the second valve 55 is opened, and the pressurized air in the air spring 34 is discharged thrugh an exhaust hole 54, and the spring constant is made low.