PURPOSE: To reduce speed change shock and ensure the durability in a frictional engaging element by changing the output of an engine in changing the speed of an automatic transmission, and completing output change when intake air amount is below a prescribed level.

CONSTITUTION: In changing the speed of an automatic transmission B where the driving output of an engine A is inputted, the output of the engine A is changed by a means (C) to reduce speed change shock due to transmission operation. According to the changing time of an automatic transmission detected by a means (D) and an intake air amount detected by a means (E), the output change of the engine A starts upon transmission start in the condition where the intake air amount is above a prescribed amount, and the output change is generally completed upon transmission completion. When the intake air amount is below a prescribed level during the output change of the engine A, a prescribed delay period is established from this time, and the output change is completed by a means (F).