The present invention provides a sodium absorption inhibitor, a potassium absorption inhibitor, and a phosphorus absorption inhibitor, and a preventive agent, a therapeutic agent and a food for diseases caused by overconsumption of common salt, potassium and phosphorus or diseases which require restriction of ingestion of common salt, potassium and phosphorus to actively and safely excrete overconsumed common salt, potassium and phosphorus excreted outside the body. R—O-A   (I) {In the formula (I), R represents a crosslinked cellulose residue and A represents a functional group a having cation-exchange ability.}