To provide a low-cost planetary roller speed changer with excellent rotation accuracy capable of easily preventing irregularities in rotation deriving from displacement between a revolution shaft of planetary roller and a rotation shaft of a carrier.

Through holes (3j and 3i) opened on the both sides of a carrier 3 are formed at the center of the carrier 3. While an end of an output shaft 4 is fitted and fixed to the opening on the output shaft side, an input shaft 1 is freely rotatably inserted into the opening of the input shaft side. By this configuration, the input shaft 1 and the output shaft 4 can be easily centered, thus preventing irregularities in rotation of the output shaft 4. Since the number of part items for centering the input shaft 1 and the output shaft 4 is small, and assembling becomes easy, the reduction of the product cost can be achieved.