Patent ID: 7361119

Claim:
A speed reducer comprising: a shaft serving as an internal member; an external gear serving as an external member, wherein the external gear reduces a speed of rotation of the shaft, and transmits the rotation to an output member; a needle bearing provided in an annular space formed between the shaft and the external gear; and a restriction member for directly limiting axial movement of the needle bearing; the needle bearing comprising: a retainer of a substantially-annular shape having a plurality of substantially-rectangular restriction holes therein extending in an axial direction of the retainer so as to be spaced at a predetermined interval in a circumferential direction of the retainer; and a plurality of needle rollers each of which is received in the respective restriction hole at a radially-outward end portion thereof and is held in rolling contact with both of an inner periphery of the external member and an outer periphery of the internal member, wherein a sliding-contact region, to which the restriction member is allowed to be brought into direct sliding contact, is formed on an end surface of each of the plurality of needle rollers for limiting axial movement of the needle rollers; and an inner diameter of the retainer is larger than an outer diameter of the restriction member disposed close to the needle rollers, so that a radial inner end of the retainer is spaced radially outwardly from a radial outer end of a sliding-contact region.