To detect the backward-forward acceleration of a vehicle with accuracy by eliminating the influence of the surface gradient of a road from the detected results of a forward-backward G sensor which detects the forward- backward acceleration of the vehicle.

A device for detecting forward-backward acceleration of vehicle not only reads the detected results of a forward and backward G sensor 12, but also those of a gradient sensor 13. The device calculates the component of the gravitational acceleration of its own vehicle in the forward-backward direction of the vehicle based on a gradient value θ detected by means of the sensor 13 and uses the component as a correction value Δα. Then the device corrects the detected results of the sensor 12 by removing the influence of the surface gradient of a road by subtracting the correction value Δα from the detected results of the sensor 12.