To precisely attain a target transmission gear ratio in a device where a transmission gear ratio varying means is controlled according to a target transmission gear ratio by sensing a temperature of a continuously variable transmission, and correcting the controlling rate of the transmission gear ratio varying means by dislocation of the transition gear ratio caused by thermal expansion difference of parts.

During driving a car, a transmission controller 2 reads a throttle opening TVO and an engine speed Ne, and also reads an input shaft rotational speed Nt and an output shaft rotational speed No from a continuously variable transmission 10. A target transmission gear ratio is computed first from a target input rotational speed and the output shaft rotational speed. An actual target transmission gear ratio is computed from the target transmission gear ratio and an estimated engine torque while considering torque shifting of the continuously variable transmission 10. Number of controlling steps of a step motor is obtained from the actual target transmission gear ratio. In this case, whether a temperature sensors 5 is normal or not is checked. When it is normally operated, temperature compensating steps are computed from a map based on oil temperature. The target step number is corrected based on the computed steps.