When a speed of a vehicle is less than 8 km/h, an upshift determination condition is established, an idle switch signal is turned off, and a downshift is detected, an operating speed of the step motor is limited. Thereby, since the operating speed of the step motor is limited even when the vehicle is rapidly decelerated and re-accelerated before a pulley ratio is returned to a lowest value Lo, a shift speed of the downshift performed in the re-acceleration is lowered, and no slippage occurs in a V-belt between pulleys.