PURPOSE: To achieve both comfortableness when an input from a road surface is large, and a flat feeling when the input from the road surface is small by detecting a relative displacement between springing and unspringing, and performing control in accordance with the relative displacement.

CONSTITUTION: Springing vertical acceleration sensors 1 are provided in a car body at close positions to four shock absorbers SA1-SA4. A control unit 4 is provided to take inputs of signals from the vertical acceleration sensors 1, and output drive control signals to pulse motors 3 of the shock absorbers SA1-SA4 respectively. For each shock absorber SA1-SA4 a stroke sensor 8 is provided to detect a stroke quantity of the shock absorber SA1-SA4 by determining a distance to a reflection plate 8a based on a time till detection light emitted downward is applied to the reflection plate 8a provided at an upper part of an ouer cylinder 33 and returns. Relative displacement of the on-spring vertical acceleration can thus be restricted.