A method for manufacturing a structure body having a resin molded body; the resin molded body comprising: a front wall and a back wall facing each other with a gap therebetween, and a surrounding wall connecting surrounding edges of the front wall and the back wall; a first main body portion and a second main body portion; and a hinge portion; wherein the first main body portion and the second main body portion are connected at the hinge portion with each other so as to be rotatable with respect to each other; the hinge portion comprises a first thin portion, a second thin portion, and a thick portion; the thick portion is a portion being larger in thickness than the first thin portion and the second thin portion; the first thin portion, the second thin portion, and the thick portion elongate in a longitudinal direction of the hinge portion; and the thick portion is sandwiched by the first thin portion and the second thin portion in a width direction of the hinge portion; the structure body further comprising an outer surface material provided so as to extend over the first main body portion, the hinge portion, and the second main body portion, wherein the outer surface material is integrally molded with the resin molded body; the method comprising the steps of: an extruding step, a shaping step, and a clamping step; wherein: in the extruding step, a first resin sheet and a second resin sheet are extruded in between a first mold and a second mold; each of the first mold and the second mold is provided with a cavity (21a, 31a); in the shaping step, the first resin sheet and the second resin sheet are shaped along an inner surface of the cavity (21a, 31a) of the first mold and the second mold in a condition where an outer surface material is arranged in between the first resin sheet and the first mold; in the clamping step, the first mold and the second mold are clamped; the second mold is provided with a protrusion to form the hinge portion, tip surfaces (31c1) corresponding to the first and second thin portions (5a, 5b) and a groove (31c2) corresponding to the thick portion are provided at a tip of the protrusion; and a portion compressed by the tip surfaces (31c1) of the protrusion becomes the thin portions (5a, 5b), and a portion facing the groove (31c2) becomes the thick portion. a front wall and a back wall facing each other with a gap therebetween, and a surrounding wall connecting surrounding edges of the front wall and the back wall; a first main body portion and a second main body portion; and a hinge portion; wherein the first main body portion and the second main body portion are connected at the hinge portion with each other so as to be rotatable with respect to each other; the hinge portion comprises a first thin portion, a second thin portion, and a thick portion; the thick portion is a portion being larger in thickness than the first thin portion and the second thin portion; the first thin portion, the second thin portion, and the thick portion elongate in a longitudinal direction of the hinge portion; and the thick portion is sandwiched by the first thin portion and the second thin portion in a width direction of the hinge portion; the structure body further comprising an outer surface material provided so as to extend over the first main body portion, the hinge portion, and the second main body portion, wherein the outer surface material is integrally molded with the resin molded body; the method comprising the steps of: an extruding step, a shaping step, and a clamping step; wherein: in the extruding step, a first resin sheet and a second resin sheet are extruded in between a first mold and a second mold; each of the first mold and the second mold is provided with a cavity (21a, 31a); in the shaping step, the first resin sheet and the second resin sheet are shaped along an inner surface of the cavity (21a, 31a) of the first mold and the second mold in a condition where an outer surface material is arranged in between the first resin sheet and the first mold; in the clamping step, the first mold and the second mold are clamped; the second mold is provided with a protrusion to form the hinge portion, tip surfaces (31c1) corresponding to the first and second thin portions (5a, 5b) and a groove (31c2) corresponding to the thick portion are provided at a tip of the protrusion; and a portion compressed by the tip surfaces (31c1) of the protrusion becomes the thin portions (5a, 5b), and a portion facing the groove (31c2) becomes the thick portion. in the extruding step, a first resin sheet and a second resin sheet are extruded in between a first mold and a second mold; each of the first mold and the second mold is provided with a cavity (21a, 31a); in the shaping step, the first resin sheet and the second resin sheet are shaped along an inner surface of the cavity (21a, 31a) of the first mold and the second mold in a condition where an outer surface material is arranged in between the first resin sheet and the first mold; in the clamping step, the first mold and the second mold are clamped; the second mold is provided with a protrusion to form the hinge portion, tip surfaces (31c1) corresponding to the first and second thin portions (5a, 5b) and a groove (31c2) corresponding to the thick portion are provided at a tip of the protrusion; and a portion compressed by the tip surfaces (31c1) of the protrusion becomes the thin portions (5a, 5b), and a portion facing the groove (31c2) becomes the thick portion.