Provided is a water absorbent resin that is useful to sanitary materials such as a disposable diaper, a sanitary napkin, and a blood absorbent for medical use each having a higher liquid permeability and a higher water absorbing speed. Further provided is a water absorbent resin powder that is useful to sanitary materials such as a disposable diaper, a sanitary napkin, and a blood absorbent for medical use each having a smaller amount of return of a liquid and a higher heat retaining property. A gel grinding device (100) to be used to produce a water absorbent resin, includes: a screw (11)； a feed opening (14)； an extrusion opening (16)； a porous plate (12)； and a barrel (13), the screw (11) including: a rotating shaft (22)； and a flight, and the screw (11) satisfying at least one of specific parameters.
