To improve estimation accuracy of a gradient resistance, in a gear shift controller estimating the gradient resistance of a vehicle and executing gear shift control.

In this controller, an acceleration ΔVSP is calculated from a change amount of a vehicle speed VSP in a time of 200 ms, while average values F0, R0 of a drive force F and an air resistance R calculated at every 10 ms in the latest time of 200 ms are calculated. An acceleration resistance Rα is calculated on the basis of the acceleration ΔVSP, and the gradient resistance (the gradient resistance = F0-R-Rα) is calculated on the basis of the acceleration resistance Rα, the average drive force F0 and the average air resistance R0. When the gradient resistance is larger than a prescribed value, a shift step is decided by use of a gear change map for an upward slope.