A continuously variable V-belt transmission includes a lateral pressure control valve for controlling the lateral pressures of a drive pulley and a driven pulley, and a controller for controlling the lateral pressure control valve. The controller calculates a target belt transmission torque by adding a predetermined marginal torque to a transmission torque calculated based on a signal detected from a driving condition of a vehicle, and obtains, by means of a signal converter, a control signal for controlling the lateral pressure control valve. With this arrangement, it becomes possible to prevent slippage between the belt and pulleys and to produce a most appropriate clamping force even when the lateral pressure control oil pressure is varied due to secular and environmental changes in the pulley lateral pressure control valve, whereby the transmission is rendered durable, efficient in fuel consumption and highly reliable.