A method of producing a water-absorbent resin, the method comprising: reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in one or more steps, wherein the polymerization is performed in the presence of an azo based compound, a peroxide and an internal crosslinking agent in each step; and performing post-crosslinking with a post-crosslinking agent to form the water-absorbent resin, wherein the water-soluble ethylenically unsaturated monomer comprises partially neutralized acrylate monomers in an amount of 70 to 100 mol% relative to the total amount of water-soluble ethylenically unsaturated monomers, and wherein the water-soluble ethylenically unsaturated monomer comprises (meth)acrylic acid and/or salts thereof, wherein the internal crosslinking agent consists of a polyglycidyl compound, and the post-crosslinking agent consists of a polyglycidyl compound, wherein the azo based compound is present in a proportion of 60 mass% or more and 80 mass% or less in the total used amount of the azo based compound and the peroxide, wherein the resin has a water-absorption capacity of physiological saline under a load of 4.14 kPa of 16 mL/g or more, a mass proportion of particles from 150 to 850 μm relative to the whole proportion is 85 mass% or more, moreover a mass proportion of particles from 300 to 400 um relative to the whole proportion is 20 mass% or more, the centrifuge retention rate is 38 g/g or more, tanδ measured by sizing the 300 to 400 μm particles of the water-absorbent resin is from 1.00 × 10 -2 to 2.00 × 10 -2; and an absorption capacity elasticity index represented by formula of 68000 or more: absorption capacity elasticity index = storage elastic modulus [Pa] × centrifugal retention rate [g/g] wherein the water-absorption capacity of physiological saline under the load of 4.14 kPa of 16 mL/g, the centrifuge retention rate, the tanδ, and the storage elastic modulus are measured as described herein. wherein the water-soluble ethylenically unsaturated monomer comprises partially neutralized acrylate monomers in an amount of 70 to 100 mol% relative to the total amount of water-soluble ethylenically unsaturated monomers, and wherein the water-soluble ethylenically unsaturated monomer comprises (meth)acrylic acid and/or salts thereof, wherein the internal crosslinking agent consists of a polyglycidyl compound, and the post-crosslinking agent consists of a polyglycidyl compound, wherein the azo based compound is present in a proportion of 60 mass% or more and 80 mass% or less in the total used amount of the azo based compound and the peroxide, wherein the resin has a water-absorption capacity of physiological saline under a load of 4.14 kPa of 16 mL/g or more, a mass proportion of particles from 150 to 850 μm relative to the whole proportion is 85 mass% or more, moreover a mass proportion of particles from 300 to 400 um relative to the whole proportion is 20 mass% or more, the centrifuge retention rate is 38 g/g or more, tanδ measured by sizing the 300 to 400 μm particles of the water-absorbent resin is from 1.00 × 10 -2 to 2.00 × 10 -2; and an absorption capacity elasticity index represented by formula of 68000 or more: absorption capacity elasticity index = storage elastic modulus [Pa] × centrifugal retention rate [g/g] wherein the water-absorption capacity of physiological saline under the load of 4.14 kPa of 16 mL/g, the centrifuge retention rate, the tanδ, and the storage elastic modulus are measured as described herein.