Abstract: The present invention provides a combined injection molding product including a primary resin molding product (1) and a secondary injection molding product (2), which attain improved adhesion to each other and enhanced air tightness therebetween. The present invention enables selective and local application of compression pressure upon shaping a combined injection molding product by forming, through injection, a secondary resin molding product (2) onto a primary resin molding product (1). The method includes applying a compression pressure on a secondary resin molding product (2) side, to thereby improve adhesion between the primary resin molding product (1) and the secondary resin molding product (2) and air tightness therebetween, wherein portions at which the secondary resin molding product (2) is united with the primary resin molding product (1) with poor adhesion are compressed selectively and locally.