Disclosed is a basket 50 that is located within a basket containment vessel, into which a boric acid solution capable of dissolving a pH adjuster flows, and can allow a pH adjuster solution to flow out by the inflowing boric acid solution. The basket 50 includes a plurality of containment units 71 stacked in a vertical direction with a predetermined first space L1 therebetween. The pH adjuster can be stored in each of the containment units 71. Also disclosed is a pH adjusting device including the basket 50, the basket containment vessel in which the basket 50 can be contained and in which cooling water can be stored, and an overflow pipe that, within the basket containment vessel, allows the pH adjuster solution that is obtained from the pH adjuster dissolved in the cooling water to flow out.