A carcinogenesis inhibitor having no side effect and having an excellent effect by oral administration. A carcinogenesis inhibitor containing a hydantoin derivative or a pharmaceutically acceptable salt thereof as an active ingredient shows an inhibiting action for polyp formation and for cell proliferation, and has no side effect and highly safe whereby it is very highly useful as a pharmaceutical agent and a food such as supplement which prevent the occurrence and progress of cancer, inhibits the recurrence and metastasis of cancer and further achieves the therapeutic effect.
