A gear device includes an internal gear, a flexible external gear, and a wave generator. The wave generator has an elliptic cam and a bearing. An inner ring has an inner ring raceway surface which a plurality of balls are in contact with, and a pair of inner ring shoulder parts. At a position of a minor axis, a first inner ring shoulder part has a greater height than a second inner ring shoulder part. At a position of a major axis, the second inner ring shoulder part has a greater height than the first inner ring shoulder part.