A vehicle-supervising electronic control unit (VS-ECU) measures driving torque, which is outputted from an engine to a drive shaft through an automatic transmission. The VS-ECU measures road surface transmission torque based on rotation speeds of driving wheels of a vehicle, vehicle body speed and driving wheel torque, which are measured in advance. The VS-ECU compares the driving torque with the road surface transmission torque. If it is determined that the driving torque is greater than the road surface transmission torque, the VS-ECU estimates an opening degree of an air bypass valve for controlling the driving torque so that a difference between the driving torque and the road surface transmission torque is decreased.