Recently, harmful ion, phosphoric acid ion, nitrate nitrogen and fluoride ion is contained so much in agricultural effluent and industrial waste water.  This causes a serious problem for the environmental protection of river and sea.  From these situations, it is desired to develop an efficient adsorbent for various anions. We try to develop a new cheap adsorbent having a high capacity for adsorbing several anions selectively.  Iron oxyhydroxide was precipitated by dropping NaOH aqueous solution into iron chloride aqueous solution under a strict control kept at pH=5, and then calcinated at low temperature.  The internal surface area of FeOOH prepared was over 200m²/g.  The FeOOH consisted of beta-crystal and amorphous structures.  Various anions, F^-, PO₄^3-, NO₃^- and SO₄^2-, could be adsorbed by thus prepared porous FeOOH.  The equilibrium amounts adsorbed by the porous FeOOH were several ten times larger than those by conventionally used adsorbent.  For example, more than 100 mg/g of phosphoric acid ion could be adsorbed.  In addition, the FeOOH developed was the first adsorbent to adsorb fluoride ion completely in the presence of other anions.  From several investigations, it was clarified that the phosphoric acid ion adsorbed at the amorphous OH hydrogen bond site, on the other hand, fluoride or nitrate ion adsorb to the tunnel site of beta-crystal structure. We also confirm the ability of the FeOOH through the long run experiment of actual wastewater using continuous adsorption equipment.  Thus, it was clarified that the proposed adsorbent was effective for an efficient treatment of anions in wastewater.