An engine control system correctly determines when a vehicle overturns and includes a vehicle inclination angle detector arranged to detect an inclination of a vehicle relative to a horizontal plane, a cumulative-duration-of-inclination detector arranged to detect a cumulative duration for which an inclination angle detected by the vehicle inclination angle detector is greater than a predetermined angle, a rider's operation detector arranged to detect whether or not a rider is operating the vehicle, and an engine cut off device arranged to stop an engine of the vehicle when it has been determined that the vehicle has overturned, based on an output of the cumulative-duration-of-inclination detector indicating the cumulative duration for which the inclination angle detected by the vehicle inclination angle detector is greater than the predetermined angle, and an output of the rider's operation detector indicating that the rider is operating the vehicle.