An apparatus produces a resin product which includes a first resin layer partially covered with a second resin layer so that a boundary line between the first and second resin layers is visible from the outside. The apparatus may include a first mold side having a recess, a second mold side configured and dimensioned to enclose the recess of the first mold side ,a slide core movably fitted in the recess of the first mold side, which may be movable toward the second mold side to an extracted position to define a first cavity, and may be movable rearward to a retracted position after a first resin is injected into the first cavity to form the first resin layer, thus defining a second cavity into which a second resin is injected to form the second resin layer, the slide core including a dam dimensioned and configured to form a groove in the first resin layer during the formation of the first resin layer, wherein the dame partially positioned in the groove during the formation of the second resin layer, a first resin supply unit for supplying the first cavity with the first resin, and/or a second resin supply unit for supplying the second cavity with the second resin. The resin product produced by the apparatus is excellent in appearance, and obviates the post-processing formation of a tear line. Methods of forming the resin product are also described.