PURPOSE: To obtain a molding method of a centrifugal impeller which enables monolithic molding of the centrifugal impeller having a three-dimensional shape of a vane, while reducing equipment needed for a core.

CONSTITUTION: Between a main plate molding part 5 and a subordinate plate molding part 6 formed in a mold 1 of an injection molding machine, cores 9a made of water-soluble resin are provided at prescribed intervals along the circumferential direction and vane molding parts 12 extending spirally are formed in parts surrounded by the cores 9a. Then, injection molding is executed with a plastic in the mold 1 and a centrifugal impeller is molded by melting the cores 9a away from the inside of a molded product obtained by this injection molding, by making a solvent flow through the cores 9a of the molded product.