To provide a means of certifying vibration characteristics of a shock absorber in a road noise frequency region to use the shock absorber for suppressing pitching and rolling of a vehicle body as a means for suppressing noise (road noise) caused on a vehicle due to unevenness on a road surface.

A shock absorber subject for carrying a cylinder and a piston of the shock absorber by at least three elastic strings in such conditions that they are compressed mutually to a neutral position of stretching is prepared. A vibration input is applied to one end by a vibration generator. Vibration displacement on a desired part is measured by a vibration displacement measuring device.