A bladder-type jig used for manufacturing a stiffened panel structure using a hat stringer has the advantage that deformation of prepreg can be suppressed effectively, and durability of the jig can be improved so that repeated use of the jig is achieved. A body of the bladder includes a pipe-shaped portion and a coating film covering the outer peripheral surface of the pipe-shaped portion. The pipe-shaped portion is a main body portion of the body, and is made of a silicone rubber composition material such that its transverse cross-section has a trapezoidal pipe shape. Both side edge portions of an exposed wall portion corresponding to a lower base of the transverse cross-section are thickened edge portions which are greater in thickness than another wall portions. The thickened edge portions support the exposed wall portion from inward of the body, and can suppress the exposed wall portion from getting deformed inwardly.