To enable restart of an engine by detecting that a vehicle is restored to the upright position after overturning in an early state. An acceleration sensor having a detection axis laid laterally of a vehicle body is integrated into an ECU and mounted on the vehicle body. Outputs of the acceleration sensor are weighted and averaged, and when an average value exceeds an overturn threshold repeatedly, an overturn determination unit determines that the vehicle is overturned. On the other hand, when outputs of the acceleration sensor are determined to be below a restoration threshold, and the determination is repeatedly made, it is determined that the vehicle is restored from the overturned state. The engine is stopped when determination of overturn is made, while restart of the engine is enabled when determination of restoration is made. Especially, the reference value of determination is set so that determination of restoration is made at an early stage.