According to one embodiment, in order to eliminate impurities, and the like, water to be treated is passed through each of reactor vessels, phosphorus contained in the water to be treated is removed by using an adsorbent, and thereafter the liquid held in each of the reactor vessels is discharged through each of first to third treated water discharge paths, thereby eliminating the impurities, and the like derived from the water to be treated. It is possible to eliminate the influence of the impurities in the water to be treated on the discharged desorption agent liquid containing phosphorus from the phosphorus adsorbent can be eliminated, and hence it is possible to obtain a phosphorus-containing liquid containing no substance other than the recovered phosphoric matter material.