Disclosed are (1) a porous polymer particle comprising a polymer substrate having ester bonds connected to a group containing a quaternary ammonium structure through a spacer molecule, (2) an alkali-resistant, high-strength porous polymer particle having ester bonds connected to a group containing a quaternary ammonium structure through a spacer molecule, a part of the ester bonds being saponified and converted to a hydroxyl group(s), (3) a porous polymer particle comprising a polymer substrate having ester bonds connected to a group containing a quaternary ammonium structure through a spacer molecule, the porous polymer particles being treated with an alkaline solution to generate a hydroxyl and/or a carboxyl group on a surface of the substrate, (4) an anion exchanger comprising any one of the particles (1) to (3) above, (5) a packing material for anion chromatography comprising the anion exchanger (4) above, (6) a column for anion chromatography using the anion exchanger (4) above, and (7) a method for measuring anions using the anion exchanger (4) above.