To prevent hunting in transmission route change caused by fluctuation of the final gear ratio in a power train constituted to use a different transmission route in response to the final gear ratio of a continuously variable transmission.

The final gear ratio G is attained upto the minimum value GL in a low mode route and upto the maximum value GH in a high mode route, and the same final gear ratio G is duplicaredly attained for the both modes in the range between the critical values GL and GH. When the final gear ratio G is changed from a GS attainable only in the low mode to a G2 attainable in the both modes, the mode is not changed over in a shift point P to move to a high mode condition , but it is maintained even after passing through the point P to move to a low mode condition H2. The number of times and a frequency for mode change are surely reduced to prevent hunting in change-over by utilizing the duplicated range between the critical values GL and GH.