PURPOSE: To perform lockup control for setting a speed difference between both input and output shafts of a torque converter down to the specified value, without using any information concerning the speed difference.

CONSTITUTION: On the basis of input torque in a torque converter, such a target hydraulic pressure PT as making a lockup clutch turn to a torque capacity corresponding to the specified slip lockup state, is set up (S6). Then, a detected value PR (S7) by a sensor detecting the extent of hydraulic pressure acting on the lockup clutch is compared with the target hydraulic pressure PT (S8), thereby controlling a lockup solenoid so as to make the detected value PR come nearer to the target hydraulic pressure PT (S10).