PURPOSE: To prevent the generation of a section not glued effectively by forming an air passage between a skin and a core material when the skin consisting of a synthetic resin material heated and softened is glued on the core material through vacuum molding processing.

CONSTITUTION: The composite product is manufactured in such a manner that the skin 4 consisting of the plastic material heated and softened is placed on the core material 10 through adhesives 5, air existing between the core material 10 and the skin 4 is sucked and removed through air vent holes 6 previously formed to the core material 10 and the skin 4 and the core material 10 are glued integrally. In this case, the surface opposing to the skin 4 of the core material 10 is shaped in an uneven surface 8 form or concave grooves 9 reaching the air vent holes 6 are molded onto the opposing surface. Accordingly, when the core material 10 and the skin 4 are glued, the air passages are formed between the both, air is not confined and the generation of the section not glued is prevented.