Impeller manufacturing method and impeller flow path elongation jig

An impeller manufacturing method comprising:

• an impeller forming step of integrally forming an impeller by an additive manufacturing method using a metal powder, the impeller including a disk which has a disk shape about an axis, a plurality of blades which are formed on a surface facing a first side in an axial direction of the disk with gaps therebetween in a circumferential direction about the axis, and a cover which covers the plurality of blades from the first side in the axial direction;
• an HIP processing step of processing the impeller, which is formed in the impeller forming step, by a hot isostatic pressing;
• and
• a flow path polishing step of causing a polishing fluid containing abrasive grains to flow through a flow path formed between the disk, the cover, and the blades in the impeller after the HIP processing step while pressurizing the polishing fluid to perform fluid polishing,
• wherein in the flow path polishing step, a flow path elongation jig having an elongation flow path which extends to elongate the flow path by communicating with an outlet of the flow path is mounted radially outside the impeller and the fluid polishing is performed.