A first acceleration sensor is arranged on a vehicle body for detecting an acceleration signal of the vehicle body and a second acceleration sensor is arranged on a wheel-side axle part for detecting an acceleration signal of the wheel-side axle part, the vehicle body and the wheel-side axle part execute relative movement with respect to each other. The wheel acceleration signal and the body acceleration signal are each integrated twice to form respective distance signals. The difference between the two distance signals at a first time (t.sub.0) is determined and stored as a gap value. A second distance signal difference is determined at a second time (t.sub.1) for a new gap value. When the wheel-side axle part reaches a reference position with respect to the vehicle body during the relative movement between the axle part on the wheel side and the vehicle body, a switching signal is generated and is used as a reference signal for determining the absolute position of the wheel side axle part along with the difference calculations.