This invention relates to an immunomodulator comprising, as an active ingredient, (S)—N-(4-amino-5-(quinolin-3-yl)-6,7,8,9-tetrahydropyrimido[5,4-b]indolizin-8-yl)acrylamide represented by Formula (I) or a salt thereof and a pharmaceutical composition for the prevention or treatment of a disease that can be ameliorated via immunomodulation.
