PURPOSE: To decrease unfavorable steering feeling by not giving a sudden impact force to a driver, and reduce the distortion of a rubber bag main body and improve the durability by providing a device to resist to distortion, at an area of the rubber bag main body, where distortion generates when the vehicle is braked.

CONSTITUTION: A rubber bag main body 3 in which a fluid Q is encapsulated is constituted of an upper base material 7a, of a rubber state elastic body for which a fiber reinforcing layer 5 is covered by a rubber material 6, and a lower base material 7b into a bag shape, and at a part of the side area, a feeding/discharging port 5, from which feeding and discharging of the fluid Q are performed, is provided. To the upper base material 7a and lower base material 7b of the rubber bag main body 3, distortion is generated due to moving of the fluid when a vehicle 1 is braked, so at the central upper surface of the upper base material 7a of the rubber bag main body 3, where the generation of distortion is great, a plurality of rubber state elastic body sheets 8 which are made of the same material are laminated to reinforce the upper base material 7a, and it is constituted in such a manner that the rubber bag main body 3 resists against distortion which is generated when the vehicle 1 is braked. A sudden impact force is not given to a driver, and unfavorable steering feeling is reduced, and the durability is improved by decreasing distortion of the rubber bag main body, which is generated at the time of braking.