To reduce damage in amenity as much as possible under bad traveling road characteristics by providing a change device for adjusting a vibration damper and deciding the change of the vibration damper adjustment according to the time elapse of acceleration of practical intervals.

As for a vehicle having an air spring, an output 5 of a block 1 and an output 7 of a block 2 are supplied to a block 3 as an input and a comprehensive damping demand is calculated by changing the damping demand of a structural part according to a bad road characteristic value. An acceleration of practical intervals is summed in a time window forming a starting point and fluctuating so as to remove long-wave components. In this change, the bad road characteristic value sets the optimum conditions to correct the damping demand of the structure part and the direct detection of the damping force or a damper speed under a substitutional condition is eliminated so that the bad road characteristic value is set to the substitutional quantity substituted for the damping force. That is to say, a large bad road characteristic value expresses a lot of components of the high frequency shaft vibration and large damper speed and damping force are generated.