To light weight and prevent abnormal vibration caused by invasion of rainwater by manufacturing a blade part so as to form an a hollow part in an inside by fusing and bonding two pieces, and filling a resin material having a low specific gravity in the hollow part.

In an impeller for a blower wherein a plurality of, for example, three blades are disposed around a hub, each blade is composed of an upper cover pieces 3 made of PP(polypropylene), and an impeller piece 5 which is similarly made of PP, and which is formed in a pan shape integrally formed with a hub 4. Each upper cover shaped piece 3 and the impeller piece 5 are integrally joined with each other at a fusing part 6 in a circumferential edge of the upper cover shaped piece 3 by fusing with ultrasonic wave. A resin material having a low specific gravity, for example, foaming beads made of PP, are filled from a filling port into a hollow part formed between both pieces 3, 5, the foaming beads are foamed, and then, the filling port is closed by an adhesive tape and the like.