A method for treatment of disease classified as any of grade 1 to 3 according to the ICRS classification of osteoarthritis, any of grade 1 to 3 according to the Kellgren-Lawrence classification of osteoarthritis, or any of grade 1 to 3 according to the Outerbridge classification of osteoarthritis, the method includes a step of administrating an agent containing an anti-Fas IgM antibody as an active ingredient.