In general injection molding used a inclined core for the undercut processing. However, the injection mold with the inclined core has a structure complex and large. The injection mold requires an injection molding machine of higher specification. In addition, the injection molding machine should be used dedicated when the molding simultaneously different products. Thus, it can be applied in the limited space through the improvement of the inclined core for the weight reduction of the mold, it is desired to develop the tension core of the long life.