To provide a pulley unit which can build in a transmission mechanism (speeding-up mechanism) compactly having comparatively large transmission ratio, and also has the excellent durability.

A planetary roller mechanism 3 contains a sun roller 2, a ring roller 1, four planetary rollers 33, and a carrier 34. The sun roller is arranged in the central position by making the outer peripheral surface of the rotary shaft 2 as a contact transmission surface 2a. The ring roller is arranged to surround the sun roller 2 by making the inner peripheral surface of the pulley 1 as the contact transmission surface 1a. Each planetary roller 33 is arranged in the annular space between the sun roller 2 and the ring roller 1, and has the contact transmission surface 33a contacting and rotating the sun roller 2 and the ring roller 1 at the same time. The carrier 34 has four planetary rollers 33 individually pivoted with a pin 35. Since the carrier 34 is fastened to a housing 5, the planetary rollers 33 rotates in a state where revolution with the center at the sun roller 2 is stopped.