Abstract: An impeller is manufactured by forming, by molding, a first part including a base having a first annular surface with an annular shape in plan view, forming, by molding, a second part including a shroud having a second annular surface with an annular shape having an inner diameter larger than that of the first annular surface in bottom view, and a main blade portion including thin-plate-like inclined portions only extending in a radial direction further inside than an inner circumferential surface of the shroud while inclined with respect to a central axis of the shroud, the inclined portions not overlapping each other in plan view, and joining the first part and the second part together while the first annular surface and the second annular surface to face each other.