The present invention addresses the problem of providing: a separation membrane for use in the treatment of blood, which has high compatibility with blood and storage stability and does not undergo the deterioration in membrane performance even when subjected to radiation sterilization and a blood treatment apparatus having the membrane integrated therein. The present invention also addresses the problem of providing: a separation membrane for use in the treatment of blood, which exhibits good air-escaping performance during a priming processing of a blood treatment membrane and a blood treatment apparatus having the membrane integrated therein. The present invention provides: a separation membrane for use in the treatment of blood, which comprises a polysulfone-type high-molecular-weight compound, a hydrophilic high-molecular-weight compound and a polymer having a solubility of 0.5 g or less in 100 g of water at 20 DEG C and having a hydroxy group in a side chain thereof, wherein the content of the polymer falls within a specified range and a blood treatment apparatus having the membrane integrated therein.本發明之目的在於提供一種血液處理用分離膜及裝入該膜之血液處理器,該血液處理用分離膜血液相容性較高,具有保管穩定性,且即便實施放射線殺菌處理膜性能亦不劣化。本發明之目的在於提供一種同時於血液處理膜之預沖處理時具有良好之排氣性之血液處理用分離膜及裝入該膜之血液處理器。本發明提供一種血液處理用分離膜及裝入該膜之血液處理器,該血液處理用分離膜包含:聚碸系高分子、親水性高分子、及對20℃下之水100 g之溶解度為0.5 g以下之側鏈具有羥基之聚合物,且該聚合物之含量處於特定之範圍。
