A stiffened panel structure (1) includes a panel-shaped component (2) and a wire (3). The panel-shaped component (2) has a panel body (21) that curves in such a manner as to be convex outward. The wire (3) has a first end portion (31) and a second end portion (32). The first end portion (31) is bonded to a first point (211) on the inner surface (21a) of the panel body (21). The second end portion (32) is bonded to a second point (212) on the inner surface (21a) of the panel body (21). The wire (3) is strained between the first point (211) and the second point (212).