A wave generator (4) of a wave gear device (1) is equipped with a rigid cam plate (5) and a wave bearing (7). The wave bearing (7) comprises an oval raceway surface (5b) formed on the oval outer peripheral surface (5a) of the rigid cam plate (5), a flexible bearing ring (8) equipped with a circular raceway surface (8a), and multiple balls (10) inserted in the race (9) formed between oval raceway surface (5b) and circular raceway surface (8a). A ball insertion hole (11) is formed at the outer perimeter edge of the rigid cam plate (5) at a region above the minor axis Lmin of the oval where there is substantially no load; from here, the balls (10) are inserted into the race (9), after which the hole is closed by a plug (12). It is easy to insert the balls (10) through the ball insertion hole (11), and the service life of the bearing is not reduced since the ball insertion hole (11) is formed.