Provided are: a water-absorbing resin manufacturing method by which it is possible, with respect to water-absorbing resins used in sanitary materials, to obtain a water-absorbing resin that has an appropriate BET specific surface area and water absorption rate the water-absorbing resin a water-absorbing agent formed using the water-absorbing resin and an absorbent article. In this water-absorbing resin manufacturing method, when reverse phase suspension polymerisation involving two or more stages is performed on a water soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium in the presence of at least an azo compound, a peroxide, and an internal crosslinking agent, the BET specific surface area of secondary particles is controlled, said secondary particles being formed by aggregation of primary particles obtained by polymerising by adjusting the usage amount of the internal crosslinking agent during first-stage polymerisation to be within the range 0.015-0.150 millimoles per 1 mole of the water soluble ethylenically unsaturated monomer used during the first-stage polymerisation.
