To realize rotary transmission from driving body of revolution to driven body of revolution by means of friction between a driving roller and a driven roller by including high efficiency and moreover successful responsivity over long period of time.

A friction transmission gear is constructed to separate the driving body of revolution into a first axis 41 and a second axis 42. It provides cam surface 62 on the end face of the second axis 42. It also causes holding grooves 64,... provided on the end face of the first axis 41 to hold cam balls 62,... which comes into rolling contact with the cam surface 62. In this condition, when the driving body of revolution rotates, the first and second axes 41,42 relatively rotate in circumferential direction and the cam balls 62,... roll on the cam surface 61. It presses on the driven rollers the driving rollers which are provided in tip end of the first axis 41 by applying separating force in longitudinal direction on the first and second axes 41,42.