PURPOSE: To urge an awakening action to a driver and to prevent the occurrence of a trouble, by a method wherein, when the doze state of a driver in a vehicle is detected, the speed change ratio of a speed change gear is changed at a given speed change ratio width one or more times.

CONSTITUTION: A controller 54 decides meandering running due to the doze state of a driver based on a steering angle detected by a steering angle sensor 81. When it is discriminated that a car is in a meandering running state at present, setting and clearing of the number of awakening times are repeated at intervals of a given time. The number of awakening times is added to the reference target number of revolutions for a normal running range to determine the target number of revolutions Nin. When the target number of revolutions exceeds the number of revolutions Ni of an input shaft 16, a shift direction switching valve 14 and a shift speed switching valve 76 are controlled, and control of down shift (increase of a speed change ratio) of a continuously variable speed change gear 14 is repeated. Meanwhile, in the case of Min<Ni, up shift of the continuously variable speed change gear 14 is repeated at intervals of a given time. This method urges an awakening action to a driver, and enables prevention of the occurrence of a trouble due to a doze.