A steplessly variable transmission of a belt-pulley type of which speed ratio is controlled in accordance with the vehicle speed and the engine load. A control system is provided for controlling the speed ratio, when the engine throttle valve is fully closed for deceleration, in accordance with the vehicle speed so that the speed ratio is decreased in response to a decrease in the vehicle speed. The control system provides an engine brake effect in deceleration which changes in accordance with a change in the vehicle speed.
