PURPOSE: To prevent shock, by lowering the rotational speed of an engine in a short time after release of a clutch or a brake upon shift-up, to engage the clutch or the brake.

CONSTITUTION: Data such as an engine rotational speed Me, a drive shaft rotational speed Nin and output shaft rotational speed Nout, or data relating to the throttle opening degree are introduced to a CPU65 which reads in the data in accordance with a program in a ROM66, and which sets the gear range of an automatic transmission unit 4 in accordance with these data. The CPU further determines the timing of clutch engagement upon shift-change, and issues a predetermined signal. In accordance with this issued signal either one of drive circuits 62W64 is energized to the associated one of solenoid valves 33, 34, 40. When the solenoid valve 33 is actuated, a high speed clutch is released. When the valve 34 is actuated, a low speed clutch is engaged. Further, when the valve 40 is actuated, the engine speed is decreased.