To solve such problems of the conventional impeller for a pump that the flow of an impeller fluid passage is made uneven by ribs installed in a front shroud to drop the characteristic of the pump, and a gap is generated or positioning is made incorrect because each blade is arranged in and fit to the position interposed between both sides in the circumferential direction with a pair of ribs.

This impeller 3 of a pump is formed by resin molding, composed of a front shroud 3a and plural ribs 17 installed on the inside of the front shroud 3a, a gate in the resin molding is installed in the position opposite to a blade 16 in the front shroud 3a, and even in the case where the front shroud 3a is made thin, the flow of resin in resin molding is made uniform, the residual stress to the front shroud 3a is relaxed, a stress corrosion crack is not generated, and since projections are not present in the impeller fluid passage, the flow is made uniform, and the generation of strain of the front shroud 3a in molding is prevented.