Structural body of differing thicknesses, and method of manufacturing thereof

A method of manufacturing a structural body of differing thicknesses, the method comprising:

• superposing, in a plate thickness direction, a second thermoplastic resin material having a plate shape on a portion of a first thermoplastic resin material having a plate shape, and placing the second thermoplastic resin material such that rectilinear step lines intersect as seen in a plate thickness direction;
• after the placing, pressurizing and molding the first thermoplastic resin material and the second thermoplastic resin material by molding dies, while melt softening by heating the first thermoplastic resin material and the second thermoplastic resin material and making the first thermoplastic resin material and the second thermoplastic resin material integral, and, molding gradually changing portions, plate thicknesses of the gradually changing portions being gradually reduced from thicker plate portion sides toward thinner plate portion sides, by making step end surfaces running along the step lines inclined from the thicker plate portion sides toward the thinner plate portion sides, such that respective reduced thicknesses of the gradually changing portions are different from each other;
• and
• after the molding, cutting out, from a molded body molded in the molding, a region including an intersection point where the plurality of gradually changing portions intersect as seen in a plate thickness direction of the molded body, and forming an opening portion.