Patent ID: 7476174

Claim:
An eccentric oscillating-type planetary gear device comprising: an internally toothed gear, in which internal teeth having a plurality of rod-shaped pins on an inner periphery are provided by a constant pitch P; an externally toothed gear, in which at least one crank shaft hole and a plurality of through holes are formed and which has external teeth meshed with the internal teeth on an outer periphery, the external teeth having a trochoid tooth profile and being less than the internal teeth by one; a crank shaft that is inserted into the crank shaft hole and rotates to cause eccentric oscillation of the externally toothed gear; and a support body that rotatably supports the crank shaft and has a plurality of pillar portions respectively loosely fitted into the through holes, wherein a ratio obtained by dividing the diameter D of each of the pins constituting the internal teeth by the constant pitch P of the internal teeth is made smaller to an extent where tooth tops of the external teeth are radially outside the inner periphery of the internally toothed gear, and portions of the external teeth that exceed at least the inner periphery of the internally toothed gear are cut, such that interference of the external teeth and the inner periphery of the internally toothed gear is prevented.