A controller for automatic transmission that performs feedback control on a slip ratio of a lockup clutch is adapted to select one target slip ratio from a plurality of target slip ratios based on a detected automatic transmission fluid temperature of a torque converter. Thus, the controller can ensure good followability to a target value of the feedback control even when the automatic transmission fluid temperature is low. The controller can effectively prevent engine hunting and the associated vibrations of vehicle body. Therefore, the controller can accomplish a favorable slip control of the lockup clutch even if an operating range of the lockup clutch is expanded to a range where the automatic transmission fluid temperature is low.