PURPOSE: To position a retainer and steel balls smoothly by forming a tapered face at the tip part of the retainer.

CONSTITUTION: In the case of assembling an epicyclic friction type speed change gear, an elastic member 8a and an outer ring 7b are disposed coaxially with a motor shaft 4, and plural steel balls 6 are disposed at almost equal spaces apart. The elastic member 8a and the outer ring 7a are disposed in such a way as to cover plural steel balls 6. An upper casing 3 with a pinion 11 and a retainer 9 previously fitted thereto is thrust into a lower casing 2 for fixing. At this time, even if plural steel balls 6 are slightly out of the normal positions, these steel balls 6 are moved into the normal positions being guided by a tapered part 9b formed at the tip part of the retainer 9 at the time of inserting the retainer 9, so that the retainer 9 can be inserted smoothly.