Problems of high impact resistance and “warpage” of a molded body are solved by a method for producing a molded body, including: using a mold MA and a mold MB, which are a pair of male and female molds, to compression-mold a material A and a material B in contact with the mold MA and the mold MB, respectively, in which the material A contains a carbon fiber and a thermoplastic resin M1, and the material B contains a glass fiber and a thermoplastic resin M2, the molded body includes a pair of side walls and a connecting wall that is connected to the side walls, the molded body has a wave shape in cross section, and a relationship between a flatness Fa of the molded body and a height h of the side wall satisfies 0≤Fa/h<1.3.