PURPOSE: To produce a smooth torque variation in response to the intention of a driver and perform disirable lockup control under speed change control of an automatic transmission.

CONSTITUTION: A control unit carries out speed change control based on the opening of a mechanical throttle valve and an engine rotational speed N. Slippage control and lockup control are performed in response to an operational condition(composite throttle opening θG and engine rotational speed N) (step 6). A signal for driving a solenoid valve in an oil pressure circuit for controlling a speed change mechanism so as to obtain a specific speed change step set at a step S2 is generated by the control unit (step S7). Consequently, a solenoid is operated, and thereby the speed change step is achieved by connecting or disconnecting the specific frictional element. The lockup control by connection/ disconnection of a lockup clutch is performed(step S8).