A method of recovering a urine-derived nutrient salt from a used absorbent article that includes urine, the method including: an inactivating step in which a used absorbent article is immersed in a calcium compound-containing aqueous solution to inactivate a superabsorbent polymer, a separating step in which a sieve is used to separate a solid-liquid mixture that has been subjected to the inactivating step, into a first fraction containing constituent materials of the absorbent article and a second fraction containing an aqueous solution containing a calcium compound and nutrient salt, or when a precipitate containing nutrient salt has been produced in the inactivating step, into a second fraction containing an aqueous solution containing the calcium compound and nutrient salt and the precipitate containing the nutrient salt that have passed through the sieve, a precipitation step in which a precipitate containing the nutrient salt is produced by HAP method, the HAP method being a method for recovering phosphorus utilizing the phenomenon of crystallizing hydroxyapatite (Ca 10 (PO 4) 6 2) produced by reaction between PO 4 3-, Ca 2+ and OH - in solution, and a concentration step in which pH of an aqueous solution contacting with the precipitate containing the nutrient salt is adjusted to a range of 5,6 to 7,0 to dissolve at least a portion of the calcium compound other than hydroxyapatite in the precipitate and increase a hydroxyapatite content in the precipitate, wherein the method further includes, prior to the inactivating step, a water addition step in which additional water is added to the used absorbent article and the superabsorbent polymer in the used absorbent article is made to further absorb water. an inactivating step in which a used absorbent article is immersed in a calcium compound-containing aqueous solution to inactivate a superabsorbent polymer, a separating step in which a sieve is used to separate a solid-liquid mixture that has been subjected to the inactivating step, into a first fraction containing constituent materials of the absorbent article and a second fraction containing an aqueous solution containing a calcium compound and nutrient salt, or when a precipitate containing nutrient salt has been produced in the inactivating step, into a second fraction containing an aqueous solution containing the calcium compound and nutrient salt and the precipitate containing the nutrient salt that have passed through the sieve, a precipitation step in which a precipitate containing the nutrient salt is produced by HAP method, the HAP method being a method for recovering phosphorus utilizing the phenomenon of crystallizing hydroxyapatite (Ca 10 (PO 4) 6 2) produced by reaction between PO 4 3-, Ca 2+ and OH - in solution, and a concentration step in which pH of an aqueous solution contacting with the precipitate containing the nutrient salt is adjusted to a range of 5,6 to 7,0 to dissolve at least a portion of the calcium compound other than hydroxyapatite in the precipitate and increase a hydroxyapatite content in the precipitate, wherein the method further includes, prior to the inactivating step, a water addition step in which additional water is added to the used absorbent article and the superabsorbent polymer in the used absorbent article is made to further absorb water.