PURPOSE: To obtain a solidification method for producing no secondary contaminant in regard to the solidification method of a radioactive adsorbent.

CONSTITUTION: After adsorption processing, a radioactive adsorbent 4 is housed in a solidification vessel 2 as it remains filled into a basket 3, a solidifying agent 5 having fluidity in the solidification vessel 2 is injected and solidified in a vacuum atmosphere. A cappilary effect is utilized, the solidifying agent 5 penetrates a clearance of the radioactive adsorbent 4, evacuation is performed and air of the clearance of the radioactive adsorbent 4 is evacuated for the purpose of promotion of penetration of the solidifying agent 5. Furthermore the basket 3, which becomes a secondary contaminant, is housed in a solidification body and solidified together with the radioactive adsorbent 4 therein.