A first mold has a core passage, and first and second cavities in fluid communication with each other at the core passage. A second mold has first and second nozzles therein that inject first and second resins to the first and second cavities, respectively. The core member is slidable within the core passage to provide or block the fluid communication between the cavities, and has a third nozzle therein to inject a third resin to the core passage. The first and second resins are injected into the cavities. The core member is moved to block the fluid communication between the cavities, before injecting the first and second resins is completed. The third resin is injected while moving the core member to provide the fluid communication, after injecting the first and second resins is completed. The molds are separated, thereby yielding a single molded product, such as a vehicle door trim.