A therapeutic or prophylactic for H5N1 influenza is provided. Specifically disclosed is a therapeutic or prophylactic for H5N1 influenza comprising as an active ingredient a compound represented by the general formula (I): wherein R 1 and R 2 represent H or alkanoyl； X represents a halogen atom, OH, alkoxy or alkanoyloxy； and R 3 represents H or alkyl； PROVIDED THAT compounds of formula (I) wherein each of R 1 and R 2 is H, X is OH, and R 3 is H are excluded.
