A fluid machine including a shaft and an impeller, wherein the impeller has a shaft bore into which the shaft is inserted, and wherein the impeller is coupled to the shaft by an interference fit. The fluid machine further includes a positioning part provided between the shaft and the impeller, for positioning the impeller at a predetermined position on the shaft; a fitting part provided inside the shaft bore and adjacent to the positioning part, for forming the interference fit between the shaft and the impeller; and a loose-insertion part provided inside the shaft bore and adjacent to the fitting part, for forming a clearance between the shaft and the impeller.