The present invention provides: an assay method that uses a compound represented by formula (I) as a fluorescent probe molecule and that is for detecting the lipid peroxidation suppression activity of a test compound; an assay kit that uses the assay method; a screening method that uses the assay method; and a pharmaceutical composition that is for the treatment, etc. of diseases (such as age-related macular degeneration) that are induced by lipid peroxidation reactions.