To provide a novel preventive and/or therapeutic agent against a virus, disclosed is a preventive and/or therapeutic agent against a viral infection containing geranyl-geranyl acetone as an active ingredient. Also, disclosed are inducers for increasing the activity of an anitiviral factor and for protein kinase containing geranyl-geranyl acetone as an active ingredient. Moreover, a method for preventing and/or treating a viral infection which contains administering a patient a effective amount of an agent containing geranyl-geranyl acetone as an active ingredient.