A working machine having a belt-type continuously variable transmission in a working power transmission system includes a target working speed setting section for optionally setting a target working rotational speed of a working unit, a working unit speed sensor that detects an actual working rotational speed of the working unit, a speed reduction ratio regulation mechanism that regulates a minimum speed reduction ratio of a rotational speed of a driven pulley with respect to a drive pulley, and a control unit. The control unit controls a drive source rotational speed to bring the actual working rotational speed close to the target working rotational speed, obtains a minimum limit speed reduction ratio based upon a target minimum rotational speed of a drive source and the target working rotational speed, and controls the speed reduction ratio regulation mechanism to keep the minimum limit speed reduction ratio.