difference dn so as to obtain favorable running feeling and fuel consumption however with regard to the change rate di dt of speed reduction ratio thus obtained from the equation 3 the component dia dt corresponding to the predicted acceleration dv 0 dt is determined based on only the reserved power of engine e the influences of running resistance in the ascending or descending slope are not taken into account for this reason when the speed reduction ratio is controlled based on the change rate di dt of speed reduction ratio calculated by the equation 3 in the ascending slope the engine speed tends to fall under the reference speed because of increased running resistance while in the descending slope it tends to rise over the reference speed because of decreased running resistance such being the case in this ratio control aforesaid deviation from the reference speed is corrected using the difference between the predicted acceleration dv o dt and the actual acceleration dv dt thus the change rate di dt of speed reduction ratio is given by the following equation 8 where c 1 c 2 and c 3 are constants for weighting more particularly the change rate di dt of speed.