PURPOSE: To suppress occurrence of breakage due to collision against foreign matter and improve reliability by specifying the shape of an impeller made of resin, particularly the shape of tip of its blade, in the impeller made of synthetic resin in a compressor of turbo charger.

CONSTITUTION: An impeller 4 made of synthetic resin in a compressor of turbo charger consists of a long blade 21 and a short blade 22. A boss 24 which has a shaft hole 25 in which a rotary shaft is inserted is provided on the inlet side of inducer, and a back plate 26 is provided on the faces which oppose each other. The tip of blade is formed in the shape approximate to semielliptical, and the thickness of the tip of blade A is equal to a short axis a. In this case, when the ratio of a semielliptical long axis b to the short axis a is B, it is formed so as to satisfy A≥0.12B+0.25. Thus, the shape of tip of blade of the impeller made of resin is optimized, the occurrence rate of breakage due to collision against foreign matter is reduced, and compression efficiency is improved.