It is intended to provide a ceramidase inhibitor which inhibits ceramidase activity, in particular, neutral/alkaline ceramidase activity, characterized by containing, as the active ingredient, a substance obtained by treating at least one plant selected from the group consisting of plants belonging to the families Ginkgo, Curcurbitaceae, Rutaceae, Laminaria, Myrtaceae and Asteraceae; and drugs, quasi drugs, cosmetics and foods containing the above inhibitor.