To provide a new drug for treating and effective for rheumatoid arthritis.

The drug for treating rheumatoid arthritis contains a material having action for inhibiting activity of "protein kinase increased in expression in cells of an animal suffering from rheumatoid arthritis compared with cells of an animal without suffering from the rheumatoid arthritis". The protein kinase is preferably one or more protein kinases selected from the group consisting of tyrosine kinase and serine/threonine kinase. "The protein kinase increased in expression in cells of an animal suffering from rheumatoid arthritis compared with cells of an animal without suffering from the rheumatoid arthritis" is preferably selected from the group consisting of HCK, MET and RON. As active ingredients, Src family inhibitors, neutralizing antibodies against the protein kinase and MET inhibitors are concretely cited.