Provided is a water-absorbent resin that increases the diffusivity of an absorbed liquid and that makes it possible to effectively decrease the amount of reversion. The water-absorbent resin is obtained by polymerizing a water-soluble ethylenically unsaturated monomer under the presence of an internal crosslinking agent, has a saline absorption capacity of 20 ml/g or more under a load of 4.14 kPa 120 minutes after the start of absorption, and exhibits an under-load swelling degree of 70% or less after 30 minutes when the saline absorption capacity under a load of 4.14 kPa 120 minutes after the start of absorption is designated as an under-load swelling degree of 100%. The water-absorbent resin can be produced by performing the following steps in a method in which a water-absorbent resin is produced by performing reverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon dispersion medium under the presence of an internal crosslinking agent: a step in which polymerization is performed under the presence of an azo compound and a peroxide; and a step in which a water-containing gel obtained by said polymerization is post-crosslinked using a post-crosslinking agent.Se proporciona una resina absorbente al agua que incrementa la difusividad de un líquido a absorberse y que hace posible para disminuir efectivamente la cantidad de re-humectación. La resina absorbente al agua se obtiene al polimerizar un monómero no saturado etilénicamente soluble al agua bajo presencia de un agente reticulado interno, tiene la capacidad de absorción al agua de solución salina fisiológica bajo una carga de 4.14 kPa en 120 minutos transcurridos desde el inicio de la absorción al agua de 20 ml/g o más, y exhibe el grado de hinchazón bajo una carga de 30 minutos de 70% o menos cuando la capacidad de absorción al agua de la solución salina fisiológica bajo una carga de 4.14 kPa en 120 minutos desde el inicio de la absorción de agua se diseña com