A controller is provided with a lock-up capacity control means for controlling a lock-up capacity to a predetermined target capacity when a transition to a coast running state occurs, a timing means for measuring a time during which a slippage, which is a difference between a revolution speed (engine speed) of an input element and a revolution speed (turbine speed) of an output element, is within a predetermined range when the lock-up capacity is controlled to the predetermined target capacity, and a capacity learning means for making a learning-correction to the predetermined target capacity such that the time measured by the timing means is brought to a predetermined target time. By virtue of the learning-correction, it is possible to accurately control the lock-up capacity when the transition to the coast running state has occurred.