Estimated change in operating fluid volume within a primary fluid chamber over a predetermined period of time during gear change operation is calculated using a physical model. On the other hand, detected change in operating fluid volume within the primary fluid chamber over this predetermined period of time is calculated. Then the deviation of the detected change from the estimated change is calculated, and learning and correction of the difference between the characteristic stored in an electronic control unit and that of an actual flow control unit are performed based on this deviation.