A purpose is to provide a rotor manufacturing method including a magnet assembly formed of divided permanent magnet pieces to enhance insulation and advance cost reduction. The rotor manufacturing method includes forming permanent magnet pieces by dividing a permanent magnet, arranging and resin-molding the permanent magnet pieces to form a magnet assembly, and placing the magnet assembly in a rotor. The method includes placing the permanent magnet pieces all together in a molding die for use in resin-molding, and moving the permanent magnet pieces by a moving device provided in the molding die to move the permanent magnet pieces within the molding die, thereby forming the magnet assembly.