To provide an oscillation type gear device capable of prolonging lives of a recessed groove and a rolling element, and capable of restraining a noise from being generated in a concerned portion.

The rolling element used in a shaft gear is formed into a jujube shape. In concretely saying, the semi-circular cylindrical recessed groove g11 is formed in the first gear g1, and the jujube-shaped rolling element g12 is supported to allow rolling in the recessed groove g11. A substantially half of an outer circumferential face of the rolling element g12 is projected to a second gear side, because the jujube-shaped rolling element g12 is supported in the semi-circular cylindrical recessed groove g11, and a projected part is functioned as a protrusion tooth of the first gear g1.