PURPOSE: To enhance safety of traveling by controlling the drive pulley diameter into the specific maximum diameter when the vehicle speed is the specific value or more, and into the minimum specific diameter when the vehicle speed is the specific value or less, in failures of a controlling solenoid valve for controlling the driven pulley diameter.

CONSTITUTION: In a control circuit 20 of a continuously variable transmission, whether a solenoid SOL2 for controlling a drive pulley 4 is wrong or not is judged. When the result is NO, the normal transmission processing is applied, and the drive pulley pressure P1 is controlled as a function of the vehicle speed (v) and the throttle opening γ, and the driven pulley pressure P2 is controlled as a function of the gear ratio and torque T. While, when the solenoid is wrong, whether the vehicle speed is the specific value or less or not is judged. When the result is YES, the drive pulley pressure P1 is made into the minimum pressure, and the driven pulley diameter is made into the specific minimum diameter, so as to restore the vehicle speed. When the result is NO, whether the gear ratio is in the low side or not is judged. When the result is NO, the drive pulley pressure P1 is made into the maximum pressure, and the drive pulley diameter is made into the specific maximum value, so as to restore the gear ratio.