PURPOSE: To attempt the improvement of running performance in the range where running performance becomes worst due to the circulating flow of exhaust gas by restraining an exhaust gas circulating quantity when an automatic speed change gear is conditioned to a power running pattern, and furthermore when a step in speed change for low speed is judged in accordance with car speed.

CONSTITUTION: A speed change control circuit 53 which detects both a throttle opening sensor 51 and the rotary speed of an input shaft of a torque converter, controls the step in speed change of shift down and shift up in two kinds of power running pattern and an economy pattern which are set by a speed change setting device 55. A signal F is outputted from the speed setting device only when the speed change pattern is conditioned to the economy one, and when the step in speed change is conditioned to a low speed step, a three-way switch-over valve 26 opens an exhaust gas modulator valve 23 to atmosphere through a switch 40 which is closed when the step in speed change is conditioned to a low speed step, for increasing the circulating flow of exhaust gas at the time of acceleration.