PURPOSE: To reduce the undershoot of an internal combustion engine by increasing an intake air quantity in a bypass which connects the upper and lower courses of a throttle valve in an intake passage when an automatic transmission is shifted to a condition to output the driving force of said internal combustion engine.

CONSTITUTION: Normally, a control valve M6 is controlled by an internal combustion engine speed control means M7. For example, although the throttle valve M4 of an intake air passage M3 is completely closed at the time of idling, the control valve M6 is being feedback controlled so that the engine speed of an internal combustion engine M2 is at a defined target value. On the other hand, when it is detected that the condition of an automatic transmission M1 is shifted to a condition that it can transmit the output of the internal combustion engine M2 to a wheel side, the control valve M6 of the bypass M5 is opened wider controlling an air quantity to be temporarily increased, by a quantity increasing means M8.