PURPOSE:To obtain optimal steering characteristics according to the variations of loads by a method in which a fluid path area variable-type attenuation variable dumper unit is provided, and during the high loading, the ratio of the front wheel dumper attenuation to the rear wheel dumper attenuation is increased. CONSTITUTION:Signal 4a from a load sensor 4 is put in a controller 3. When the controller 3 receives a load signal above a set load, a drive signal 3a is sent out to actuators 2a, and the attenuation CR of the fluid path area variable dumper units 2a for the rear wheels is made smaller. In this case, since the attenuation CF of the dumper units for the front wheels is invariable, CF/CR ratio becomes greater and the under steer becomes stronger. At the time of low loading, CF/CR ratio is made smaller. Therefore, optimal steering characteristics according to loads can be obtained.