PURPOSE: To stably obtain at low cost high-purity iron oxide for ferrite etc. independent of the grade of the raw ore, by wet classification of hematite ore and/or magnetite ore followed by gravity concentration to produce purified ore which is subjected to polishing process.

CONSTITUTION: A raw material 1 such as hematite ore and/or magnetite ore is freed from foreign substances through a screen 2 followed by feeding, via a concentration regulation tank 3A, to a cyclone 6 to carry out wet classification. Thence, a fraction of large size 6A is introduced into an agitation tank 8A, while the other fraction of smaller size 6B into a settling separation tank 7 to feed the subfraction of larger size 7A into a second agitation tank 8B. The both fraction 6A and subfraction 7A are fed to coarse particle- and fine particle-table dressing machines 9, 10, respectively, to performs gravity concentration. The resulting purified ores 11A and 12A are subjected to concentration regulation in a tank 3B followed by introduction into a polishing equipment 4 to eliminate the impurities on the surface of the ore and perform polishing to an average particle size of 32 to 12μ followed by feeding to a washing agitation tank 13 to carry out washing and send to the following processes where the corresponding various treatments are applied followed by making into the product 21.