| CPC F16H 1/48 (2013.01) | 5 Claims |

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1. A planetary gear mechanism, comprising: a plurality of pinion gears that is held rotatably and revolvably; and an object gear that meshes with the pinion gears, wherein
the object gear includes a plurality of low rigidity portions, in which a section modulus in a radial direction of the object gear is small, at predetermined intervals in a circumferential direction of the object gear,
a plurality of teeth of the object gear includes a thermally-treated distortion portion in which an accumulated pitch error based on thermal treatment was changed,
the object gear includes a base portion and a gear portion that is fashioned on an outer peripheral face or an inner peripheral face of the base portion, and
the low rigidity portions include a groove that is fashioned on one face out of the outer peripheral face and the inner peripheral face of the base portion that is a face on an opposite side from the gear portion.
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