Provided is a device for manufacturing a rotor core with less magnetic flux leakage, a method for manufacturing the rotor core, and a rotor structure. Included are a first mold including a fitting recess that fits and holds a laminated iron core in which a magnet is inserted into a magnet insertion hole; a second mold that clamps and seals the laminated iron core together with the first mold; a resin injection unit that is provided to the second mold and injects a resin material in the magnet insertion hole by using a molding machine; and a protrusion that is inserted into the magnet insertion hole by a predetermined insertion amount, and positions and holds the magnet by an end of the magnet being brought into contact with the protrusion, in a state of the first mold and the second mold being clamped.