To provide a planetary reduction gear by the friction transmission, which eliminates any unnecessary friction force without any load of transmitting the friction force on a carrier, stabilizes the motion by the shape of a planetary roller, and enables the very consistent rotational force and the extensively improved transmission efficiency.

The planetary reduction gear comprises: a plurality of planetary rollers forming two conical surfaces on both sides of a cylindrical surface parallel to the center of rotation of an input shaft; a fixed disk having a circular inner surface in contact with one conical surface of the planetary roller; a low-speed disk having a circular inner surface in contact with the other conical surface; a drive roller having a cylindrical part in contact with the cylindrical surface of the planetary roller; a carrier member holding the plurality of planetary rollers within the same plane of rotation; and a compression spring for urging the low-speed disk to the fixed disk side.