An object of the present invention is to provide a separation membrane for blood processing having high blood compatibility and storage stability and membrane performance that rarely deteriorates even if irradiation sterilization treatment is applied, and provide a blood processing apparatus having the membrane installed therein. The present invention is also directed to providing a separation membrane for blood processing having satisfactory air-bleeding during priming treatment of the blood processing membrane, and providing a blood processing apparatus having the membrane installed therein.The present invention provides a separation membrane for blood processing, comprising a polysulfone polymer, a hydrophilic polymer and a polymer having a hydroxy group in a side chain and having a solubility of 0.5 g or less in water (100 g) at 20°C, in which the content of the polymer falls within a specific range, and a blood processing apparatus having the membrane installed therein.
