Included are a first board and a second board that include hard polyurethane foam layers and formed respectively in spaces sandwiched between pairs of thin plates, and a coupling member having a porous structure where a recessed groove is formed, parts of the coupling member being arranged in the spaces. The hard polyurethane foam layers are also formed in gaps between the thin plates and the coupling member to join the boards to the coupling member. Consequently, the step of molding the first board can mold, join, and integrate the boards, and mold a bendable, lightweight, and very strong vehicle interior board.