A bladder bag is a mold for molding inside of a composite material structure. The composite material structure includes a narrow portion formed by narrowing a part of the inside and a space portion formed so as to be adjacent to the narrow portion. The bladder bag includes a bladder bag main body and a cord-like member. The bladder bag main body includes a narrow molding portion for molding the narrow portion of the composite material structure, a space molding portion for molding the space portion of the composite material structure, and an air intake for introducing air. The cord-like member is provided inside the bladder bag main body, passes through the narrow molding portion from the air intake, and is connected to an inner surface of the space molding portion.