A wave gear device (30) uses, as a bearing which supports a first rigid internally-toothed gear (31) and a flexible externally-toothed gear (33) so as to be capable of rotation relative to each other, a composite roller bearing (38) equipped with a first roller (53) and second roller (54) for thrust bearing use and a third roller (55) for radial bearing use. Compared to a cross roller bearing or an angular bearing, the composite roller bearing (38) can be implemented as a highly rigid bearing in a small installation space. The first rigid internally-toothed gear (31) and the inner ring portion (51) of the composite roller bearing (38) are formed integrally as a single component, so an attachment part for connecting these members is not necessary. A highly rigid, flat wave gear device can be achieved.