In an apparatus for controlling a pulley side-pressure of a belt type continuously variable transmission mechanism provided, in series with a starting clutch, in a transmission of a vehicle having a function of stopping engine idling so that an engine is automatically stopped, if the vehicle start-up is controlled from the state of engine stopping in an ordinary way in which the pulley side-pressure is determined by that belt transmission torque corresponding to an output torque of the engine which is obtained by the rotational speed and the negative suction pressure of the engine, the pulley side-pressure becomes excessive by wrong judgement that the engine output torque is large, because the negative suction pressure is small at the beginning of the engine starting. The durability then deteriorates and the specific fuel consumption becomes poor. As a solution, at a vehicle start-up from the state of engine stopping, a belt transmission torque corresponding to that transmission torque of the starting clutch which is obtained by the engaging force of the starting clutch is compared with a belt transmission torque corresponding to the engine output. The pulley side-pressure is each controlled based on that transmission torque of the drive pulley corresponding to the smaller belt transmission torque and on the transmission torque of the driven pulley.