The present invention relates to an anti-viral agent comprising a compound represented by the following formula (I): (wherein X represents CH, a nitrogen atom, an oxygen atom, or a sulfur atom； Y and Z are the same or different and each represents a nitrogen atom or C&mdash；R8, and at least one of them represents a nitrogen atom； R1 to R8 are the same or different and each represents a hydrogen atom, a linear C1-10-hydrocarbon group, a hydroxy group, or a substituted or unsubstituted benzyl group； and, when X represents an oxygen atom or a sulfur atom, R5 is absent), or the following formula (II): (wherein X&prime； represents CH or a nitrogen atom； Y&prime； and Z&prime； are the same or different and each represents a nitrogen atom or N&mdash；R9, or C&mdash；R8 and at least one of them represents a nitrogen atom or N&mdash；R9； R1 to R4 and R6 to R8 are as defined above； R9 represents a hydrogen atom, a linear C1-10-hydrocarbon group, a hydroxy group, or a substituted or unsubstituted benzyl group； and, the C ring has the maximum number of double bonds at the dotted line portion) or a pharmaceutically acceptable salt thereof.
