In a flexspline (3) of a wave gear device(1), an annular flange (33) thereof is constructed from a first annular part (33a) bent at a right angle from an outer peripheral edge (32a) of a diaphragm (32), and a second annular part (33b) caused to inwardly protrude at a uniform width from a leading end of the first annular part (33a). It is possible for the annular flange to be disposed within the region where the diaphragm (32) is formed, as viewed in the direction of an axis (1a) of the device. An outer diameter can be reduced to a greater extent than with a silk hat shaped flexspline, and whena hollow wave gear device is manufactured, a hollow diameter can be more readily increased than in a case where a cup-shaped flexspline is used.