To provide a small planet roller type power transmission device excellent in durability which can cope with a high speed rotation.

The rotation of a carrier 8 is stopped by a changeover clutch 10 and the revolution of planet rollers 6, 7 is regulated and the rotation of an outer wheel 4 is increased and transmitted to a sun roller 5. When the restriction of the rotation of the carrier 8 is released, the rotation speed of the sun roller 5 is dropped and an oneway clutch 5 rotates the outer wheel 4 and sun roller 5 integrally. As the oneway clutch 19 is interposed in the torque transmission route between the outer wheel 4 and the sun roller 5 which has some rooms in the diameter direction space, the entire device can be miniaturized and lightened.