To provide various means that can be useful for the diagnosis of prophylaxis, and treatment or the like of rheumatoid arthritis.

A method etc., for screening the prophylactic or therapeutic agent for the rheumatoid arthritis includes measuring the expression level of a target gene (e.g. AREG) and evaluating whether the rheumatoid arthritis has developed in a subject; a diagnostic reagent for the rheumatoid arthritis that includes a measuring means for the target gene; a set that includes two or more measuring means for two or more target genes; a prophylactic or a therapeutic agent for the rheumatoid arthritis that includes a substance capable of inhibiting expression or functions of the target genes; a method etc., for screening the prophylactic or therapeutic agent for the rheumatoid arthritis that includes evaluation of whether a test substance is can inhibit the expression or functions of the target genes.