A first shaft end (2a) of a hollow shaft (2) of a hollow wave gear device (1) is supported by a first support bearing (4) with a collar (14) interposed therebetween which is mounted to the outer-circumferential surface of the first shaft end (2a). A second shaft end (2b) on the other end of the hollow shaft (2) is supported by a second support bearing (5). A wave plug (12) of a wave generator (10) is integrally formed with the hollow shaft (2), and a wave bearing (13) is mounted on the elliptical outer-circumferential surface (12a) thereof from the first-shaft-end (2a) side. It is possible to use a first support bearing (4) having an inner diameter larger than the outer diameter of the first shaft end (2a) as the first support bearing (4) for supporting the first shaft end (2a).
