To provide a method of manufacturing an impeller, which can smooth a polished surface without undulation, in removing an alteration layer generated on an electrical-discharge-machining surface by wet polishing after a channel is formed by electrical discharge machining.

A method of manufacturing an impeller includes a channel formation step of forming a channel 14 from an inlet 141 to an outlet 142 of a gas by electrical discharge machining, and a wet polishing step of wet-polishing an inner wall of the channel 14 by supplying a polishing liquid into the channel 14. In the wet polishing step, the polishing liquid is supplied into the channel 14 through polishing liquid nozzles 20 and 30 having a plurality of ejection holes 25 and 35 from which the polishing liquid is ejected toward the inner wall of the channel 14, and inserted into the channel 14.