It is an object of the present invention to provide a treatment agent and a preventive agent for osteoarthritis and arthritis (arthromeningitis) derived from osteoarthritis. [Means for solving problem(s)] The present invention is based on a knowledge that the use of an anti-Fas IgM antibody allows the alleviation of an osteoarthritis symptom. Specifically, the present invention is based on a knowledge that the use of an anti-Fas IgM antibody allows the inhibition of production of a cartilage matrix degrading enzyme. Furthermore, the present invention is based on a knowledge that the use of an anti-Fas IgM antibody can improve the ability to produce a cartilage matrix.
