PURPOSE: To efficiently and economically separate protein-related substances by using a separation membrane unit prepared by linking a ligand to a membranous support obtained by forming cellular glass into a tubular shape as an affinity adsorbent.

CONSTITUTION: Cellular glass is initially formed into a tubular or platy shape and a ligand having a moderate affinity for the objective substance is then linked to the resultant membranous support. The obtained support is subsequently used as a separation membrane unit and a sample liquid for separation is then passed therethrough to carry out purification by affinity chromatography. A support having 0.3-2mm thickness for the tubular shape and 0.3-1mm thickness for the platy shape and 0.3-0.6cc/g pore volume, 100-400m2/g specific surface area and 0.1-10/μm pore diameter is preferred as the aforementioned support. Furthermore, e.g. protein A for IgG is cited as the ligand.