The injection molding apparatus includes a cavity mold formed with a cavity surface for defining a cavity in which a molten injection material is injected, a core mold formed with a core surface for defining the cavity upon engagement with the cavity mold and installed to be movable forward and backward to open or close the cavity by guidance of a guide pin, an injection unit for injecting a material into the cavity during an injection process, and an injection controller for controlling a hydraulic cylinder to move the core mold forward or backward and the injection unit to inject the material into the cavity.