A parameter α(OUT) having an accelerator pedal position, a vehicle speed and a drive force as components is set according to information representing a driver's operation and information representing running environment of a vehicle. A gear is set according to the parameter α(OUT) and a map determining the gear based on the accelerator pedal position, the vehicle speed and the drive force. A gear shift line is defined such that a rate of increase of the drive force with respect to the vehicle speed is zero or more. A down-shift line is defined such that the drive force decreases with increase in accelerator pedal position. Down-shift after up-shift as well as the up-shift after the down-shift are inhibited when both a condition that an amount of change of the accelerator pedal position after last gear shift is larger than a threshold and a condition that an amount of change of the drive force after the last gear shift is larger than the threshold are satisfied.