An injection molding system is configured to produce a multi-color molded article by simultaneously or sequentially injection-molding resins of a plurality of types by means of a plurality of injection molding machines. An insert mold is mounted in a mold of a first injection molding machine and a primary molded article is molded by this injection molding machine. Thereafter, a robot arm takes out the insert mold, along with the primary molded article, from the mold of the injection molding machine and attaches it to a mold of a second injection molding machine. A two-color molded article is injection-molded by the second injection molding machine and removed as a product.