Abstract: A planetary roller type power transmission device has a first rotary shaft and a second rotary shaft which are arranged coaxially, a sun roller connected to the first rotary shaft, a stationary outer ring disposed concentrically with the sun roller, and a plurality of planet rollers disposed in the annular space between the sun roller and the stationary outer ring, the planet rollers being carried by a carrier rotatable as a unit with the second rotary shaft. The power transmission device further has a pair of mutually opposing flange-like projections formed on the outer peripheral surface of the stationary outer ring so as to pass positions adjacent to respective axial ends of the area of contact between the planet rollers and the stationary outer ring, and a tightening means operable from the outside of the transmission device and adapted to urge the flange-like projections towards each other thereby causing elastic deformation of the stationary outer ring.