A secretory function improving agent comprising, as an active ingredient, an RNAi-inducible nucleic acid capable of suppressing Giantin expression at the mRNA level, or an expression vector capable of expressing the RNAi-inducible nucleic acid in a subject of administration.Giantinの発現をmRNAレベルで抑制しうるRNAi誘導性核酸、又は該RNAi誘導性核酸を投与対象内で発現可能である発現ベクターを有効成分とすることを特徴とする分泌機能改善剤。