[Problem] To provide a stabilized liquid medicine for internal use containing a vitamin B1 derivative or salt thereof (e.g., fursultiamine or salt thereof) and vitamin B2s. [Solution] Stability is improved by further adding gallic acid, a salt thereof, or an ester thereof in a liquid medicine for internal use containing a vitamin B1 derivative or salt thereof (e.g., fursultiamine or salt thereof) and vitamin B2s.