PURPOSE: To facilitate manufacturing operation by superposing molds on one surface and the other surface of an annular balance and injecting a molding material from a nozzle, and charging it in a boss molding part and an engagement piece molding part.

CONSTITUTION: When a balance wheel is manufactured, molds 41 and 42 are superposed on one surface and the other surface of the annular balance 16 and the molding material is injected from the nozzle 44 and charged in the boss molding part 50 and engagement piece molding part 54. In this case, starting flowing-in materials decrease in speed when entering large spaces of base parts of those molding parts through inflow passages from the nozzle 44 and are pressed in edge parts, and following materials which are flowed in later pass through the inflow passages and uncharged parts of said spaces and are charged in tip parts of the molding parts. Consequently, the balance wheel 15 having a boss 17 and an engagement piece 2 formed on the annular balance 16 is obtained and the manufacturing operation is facilitated.