A method for manufacturing a rotor core includes detecting a height of a projecting portion formed on a lower die by a height detecting unit, and placing onto the lower die a core body in which a magnet insertion hole is formed such that the projecting portion is positioned in the magnet insertion hole when the height detecting unit has determined that the height of the projecting portion is within a set range. Additionally, the method includes bringing a permanent magnet in the magnet insertion hole into contact with an upper end of the projecting portion, and placing onto the core body a holding member after bringing the permanent magnet into contact with the upper end of the projecting portion. Melted resin is injected into the magnet insertion hole in which the permanent magnet has been inserted after placing the holding member onto the core body.