A transmission controller determines whether a shift returning to low, changing a speed ratio of a continuously variable transmission to the lowest when a vehicle decelerates, is being performed or not, calculates a primary pressure measured lower limit value at which a belt begins to slip actually, based on a deceleration of the vehicle and the speed ratio of the continuously variable transmission, and sets a lower limit value of a target value of the primary pressure during the shift returning to low as the primary pressure measured lower limit value.