Provide a new bis-(hydroxybenzaldehyde) compound, as well as a new polynuclear polyphenol compound derived therefrom, suitable for use as component materials for photosensitive resist compositions, component materials and hardeners for epoxy resins, developers and anti-fading agents used in thermosensitive recording materials, bactericides, fungicides, antioxidants and other functional chemical products or component materials thereof, wherein such bis-(hydroxybenzaldehyde) compound is produced by reacting in the presence of trihalogenated acetic acid catalyst or phosphoric acid catalyst a 2,6-di(hydroxymethyl)-4-alkylphenol with a hydroxybenzaldehyde expressed by general formula (14).