A heat exchanger for a blood circulation circuit comprises a hollow fiber membrane layer having a plurality of hollow fiber membranes, and a fixing portion fixing both end portions of the hollow fiber membranes from outsides of the hollow fiber membranes. The fixing portion mainly contains polyurethane, and each of the hollow fiber membranes has a heat conductive layer containing high density polyethylene, and an adhesion layer provided on an outside of the heat conductive layer, bonded to the fixing portion, and mainly containing a modified polyolefin resin.
