PURPOSE: To hold a balance weight easily and firmly by pouring an end ring material and burying the balance weight.

CONSTITUTION: A plurality of projecting sections 22a, 22b are formed to both surfaces of a semi-arcuate balance weight 22. One projecting section 22a of the balance weight 22 is brought into contact with the end surface 20a of a rotor 20, and the other projecting section 22b is gripped by one part 24a of a die-cast mold body 24 while the die-cast mold body 24 is pushed so as to surround one part of the outer circumferential surface 20b of the rotor 20. Consequently, a melted end ring material 23 by an aluminum material is poured from a pouring gate shaped to the die-cast mold body 24 and solidified, and the balance weight 22 is buried integrally. Accordingly, the balance weight 22 is held easily and firmly without executing caulking, thus acquiring stable rotary balance.