Provided is a soft capsule preparation that shows an excellent content stability of Nalfurafine or an acid addition salt thereof. The soft capsule preparation consists of a capsule core comprising Nalfurafine or an acid addition salt thereof, a hydrophobic oily base and propyl gallate, and a capsule coating comprising sodium thiosulfate.本發明提供一種具有含量穩定性優異之納呋拉啡或其酸加成鹽之軟膠囊劑。膠囊內容物中含有納呋拉啡或其酸加成鹽、疏水性之油性基劑及沒食子酸丙酯,膠囊皮膜中含有硫代硫酸鈉。