To simply, economically, efficiently produce a polyacetal resin composite molding having rigid interface adhesive properties by previously roughing a surface of a primary molding connecting part made of a polyacetal resin so that a surface area ratio to a smooth surface becomes a specific value.

In the case of forming a thermoplastic resin to the molding 1 made of a polyacetal resin, a surface (connecting surface) 3 of the molding 1 brought into contact with the formed molding 2 is previously roughed. That is, a surface area of the roughed surface is increased to 1.5 times as large as that of the smooth surface. As a method for roughing the surface of the molding, a texture transfer by a mold or a mechanical or physical forming method is used. When a flame treatment, a plasma treating, a laser emitting treatment, a sand blasting treatment, a shot blasting treatment or a liquid honing treatment is, for example, used, its operating efficiency and stability of its quality can be improved.