The purpose of the present invention is to provide an agent for preventing or ameliorating Alzheimer's disease, said agent being able to effectively suppress the accumulation of amyloid β proteins using a safe material, which has been used in foods for many years, and improve spontaneous alternation behavior change ratio. Ceramides (in particular, a glucosylceramide originating in Amorphophallus konjac) can effectively suppress the accumulation of amyloid β proteins and thus enables the prevention or amelioration of Alzheimers disease.