Abstract: The present invention relates to a stepless speed changing device and more particularly to the construction of an automatic speed changing device suitable for a vehicle or the like, the centrifugal force of said changing device is produced by the high-speed rotation of a rotating means which enables a plurality of claw blocks fitted pivotedly at a rotating disk to expand outward to increase the outside diameter thereof, and which, after the output of motive force, can produce automatically differential speed ratios of various magnitudes because of the change of said working outside diameters.