The present invention provides methods and equipments for demineralizing condensate, aiming at achieving high-purity effluent quality with a low concentration of sulfate ions derived from organic impurities leaching from cation resins in the condensate treatment by condensate demineralizers in nuclear power plants.The present invention relates to a condensate demineralizer for demineralizing condensate in a nuclear power plant, comprising a mixed bed of a strongly acidic gel-type cation exchange resin and a uniform particle size strongly basic porous anion exchange resin.