Provided is a method for efficiently recovering pulp fiber from used hygiene products that include pulp fiber and a polymer absorbent. This method is characterized by including a step for introducing the used hygiene product into a treatment tank in which an aqueous solution with ozone dissolved therein has been introduced, and a step for treating the used hygiene product while infusing water into the treatment tank at a first flow rate, extracting the aqueous solution from the treatment tank at a second flow rate and introducing a gas containing ozone into the aqueous solution in the treatment tank, thereby decomposing the polymer absorbent, lowering the molecular weight thereof, and making the same dissolvable.