A vehicle deck board 1 is molded in such a manner that a lower die 21 and an upper die 22 are clamped together in a state where foamed resins 13 and reinforcements 20 are interposed between a back surface side sheet material 16 and a front surface side sheet material 15, whereby the back surface side sheet material 16 and the front surface side sheet material 15 are welded to each other to thereby form a laminated member 26 with height-increasing bridge members included therein, compressed air is injected into an inside of the laminated member 26 with the height-increasing bridge members included therein, which is formed by welding the back surface side sheet material 16 and the front surface side sheet 15, while individually vacuum-sucking the back surface side sheet material 16 and the front surface side sheet material 15 to the lower die 21 and the upper die 22, and the laminated member 26 concerned is subjected to blow molding.