The problem of the present disclosure is to provide a method of manufacturing a rotor core by which a rotor core excellent in weight balance can be produced efficiently. A method of manufacturing a rotor core includes: acquiring weights of a plurality of permanent magnets individually; obtaining first to N th (N is a natural number equal to or greater than 2) magnet sets by combining at least one relatively heavy permanent magnet and at least one relatively light permanent magnet of the permanent magnets into one magnet set, based on the acquired individual weights of the permanent magnets; preparing a core body configured to rotate around a predetermined rotational axis, the core body having first to N th attaching locations in a row in a circumferential direction of the rotational axis; and attaching the first to N th magnet sets to any of the first to N th attaching locations one by one.