The present invention provides a multiple bed-type condensate demineralization method and apparatus for the method that are able to provide an improved treated water quality in ammonia operation by substantially reducing the cross contamination ratio during resin regeneration from the current cross contamination ratio.In the method of condensate demineralization using ion-exchange resin in a multiple-bed regime, condensate is passed through a resin layer having a multiple-bed structure in which an anion resin layer and a layer of a uniform particle size strong acid gel-type cation resin with a 10% to 16% degree of crosslinking, divided by a partition in such a manner that they do not mix with each other, are combined in alternation. The uniform particle size strong acid gel-type cation resin with a 10% to 16% degree of crosslinking is an ion-exchange resin that has a uniform particle size of 500 to 800 μm for which at least 95% of the resin particles fall in the range defined by the average particle size ±100 μm and the uniformity coefficient is less than or equal to 1.2. Ion-exchange resin that has come to require chemical regeneration is separately withdrawn and subjected to chemical regeneration by type and is returned into the originating partition.