A method of manufacturing an impeller rotor assembly including: manufacturing a cylindrical magnet in which hollow space is formed; manufacturing a magnet yoke which is assembled on the inner circumferential surface of the magnet in cylindrical form where hollow space is provided, and in which an outer diameter is 0.02 to 0.3 mm smaller than the inner diameter of the magnet; assembling the magnet and magnet yoke; and mold forming in which the assembly of the magnet and magnet yoke is integrated into the mold.