The invention provides a control device for a lock clutch of a torque converter. The control device is capable of suppressing downshift impact more effectively. According to the control device, the torque converter is used for connecting an output shaft of an engine of an automobile with an input shaft of an automatic transmission; the lock clutch is included and is capable of directly and mechanically connecting the input shaft with the output shaft; and when the automobile is in a specified driving state, the control device enables the lock clutch to be engaged at a predetermined target engagement degree. The control device is provided with a vibration judgment mechanism, an engagement degree control mechanism and an engagement degree correction calculation mechanism, wherein the vibration judgment mechanism is used for judging the degree of speed changing vibration caused by downshift after downshift; the engagement degree control mechanism is used for controlling the engagement degree of the lock clutch; and the engagement degree correction calculation mechanism is used for calculating the correction of the target engagement degree during torque control over the automatic transmission during downshift, and the engagement degree correction calculation mechanism calculates the correction of the target engagement degree according to judgment results of the vibration judgment mechanism.