An electronic control circuit calculates the actual revolution speed ratio between the driving and driven pulleys of the transmission, generates a first electric control signal corresponding to the difference between the actual revolution speed ratio and an aimed revolution speed ratio predetermined for both the pulleys in conjunction with the input torque of the input shaft and required torque for the output shaft, and generates a second electric control signal made of the sum of both an electric signal corresponding to the actual revolution speed ratio and an electric signal corresponding to the difference. A hydraulic control circuit includes a pressure oil source, a first cylinder which is provided on the input shaft and supplied with working oil from the pressure oil source to push a movable member of a driving pulley toward a fixed member thereof, a second cylinder which is provided on the output shaft and supplied with working oil from the pressure oil source to push a movable member of a driven pulley toward a fixed member thereof, a first control valve which is disposed in an oil passage for connecting the pressure oil source and a first cylinder to each other and acts on the basis of the first electric control signal to control the flow rate of the working oil supplied to or drained from the first cylinder, and a second control valve which is disposed in an oil passage for connecting the pressure oil source and the second cylinder to each other and acts on the basis of the second electric control signal to control the pressure of the working oil supplied to the second cylinder.