a rotation input disk and a rotation output disk, and

a plurality of power rollers provided between ring-shaped concave surfaces formed respectively in opposing surfaces of said input and output disks, said opposing surfaces varying a speed-change ratio by varying inclination of turning surfaces of said power rollers within a plane that includes a disk center shaft of said disks;

said stepless speed changer further comprising:

a power roller supporting shall which is provided on a turning center axis of each one of said power rollers and protrudes from between the opposing surfaces of said input and output disks to outside in a radial direction of said disks;

a movable ring that encloses at least an outside of said input disk, in which outer ends of all of said power roller supporting shafts are engaged with said movable ring, said movable ring being movable in parallel with the disk center shaft while being restricted in turning; and

an adjustment belt that encloses said movable ring, in which said adjustment belt being held by a frame body so as to make a reciprocal motion by prescribed amounts in a direction of turning thereof, and said adjustment belt moving said movable ring in parallel with the disk center shaft by said reciprocal motion thereof; and wherein

inclination of all of said power roller supporting shafts is varied by movement of said movable ring in a direction of the disk center shaft caused by the reciprocal motion of said adjustment belt.