In a demineralization apparatus, a mixed bed of a gel type cation exchange
resin having a moisture holding capacity of 41% or less or a degree of
crosslinkage of 12% or greater is employed along with a porous type anion
exchange resin. As a result, oxidation degradation of the cation exchange
resin due to hydrogen peroxide can be inhibited and the performance of the
ion exchange resins and of the condensate water demineralizer can be
stabilized and maintained for a long period of time.
