Abstract: An object of the invention is to provide a compound that can be utilized as an antiviral agent, in particular as an anti-RNA viral agent, and especially as an anti-RS viral agent. The invention provides a compound indicated by Formula (1), wherein R1 each independently represent hydrogen, halogen, hydroxyl, amino, carboxyl, C1-C6 alkyl, C1-C6 alkoxyl, C1-C6 halogenoalkyl, C1-C6 alkoxycarbonyl, C1-C6 alkylamino, C2-C5 alkenyl, C3-C6 cycloalkyl, or optionally substituted aryl; R2 each independently represent hydrogen, C1-C6 alkyl, C1-C6 halogenoalkyl, C2-C5 alkenyl, C3-C6 cycloalkyl, optionally substituted aryl or heterocyclic group; and one or more R1 may be present in the same ring, an isomer thereof, a pharmaceutically acceptable salt thereof, or a mixture of these. The compounds provided by the invention are useful as drugs for the prevention or treatment of infectious diseases by virus, especially RS virus, and in particular infectious diseases in the lower airways (e.g., bronchiolitis, pneumonia, etc.).