PROBLEM TO BE SOLVED: To provide a decontamination method and device which can remove radioactive cesium and cyanogen.SOLUTION: A radioactive cesium decontamination device comprises a radioactive cesium adsorption tower 10 filled with a cesium adsorbent carrying a ferrocyanic compound and a cyanogen adsorption tower 20 filled with an anion exchange resin and/or a chelate resin, and the radioactive cesium is adsorbed to the ferrocyanic compound, and then cyanogen is adsorbed to the anion exchange resin and/or chelate resin, so that cyanogen can be adsorbed and removed together with radioactive cesium.