PURPOSE: To provide proper completion of output change by making the back-up setting of proper transmission completion time for the change in transmission time when decelerating shock due to the transmission operation of an automatic transmission is decreased by changing the output of an engine.

CONSTITUTION: In changing the speed of an automatic transmission B where the driving output of an engine A is inputted, the output of an engine A is changed by a means C to reduce decelerating shock. According to the decelerating time of an automatic transmission B detected by a means D, output change starts upon the transmission start. The control of the output change is made according to the completion judgment results of first and second means E, F. In other words, the first means E makes completion judgment when the rotational speed of the engine A and so forth meets a prescribed completion condition. The second means F makes completion judgment when the rotational speed of the engine A and so forth becomes higher again after it has been lower once than the back-up setting point where it is higher than the level corresponding to the above completion condition by a prescribed value.