A medical heat exchanger includes a thin tube bundle 2 in which a plurality of heat transfer thin tubes 1 for letting heat medium liquid flow therethrough are arranged and stacked, seal members 3a to 3c sealing the thin tube bundle while allowing both ends of the heat transfer thin tubes to be exposed and forming a blood channel 5 which allows blood to flow therethrough so that the blood comes into contact with each outer surface of the heat transfer thin tubes a housing 4 containing the seal members and the thin tube bundle and provided with an inlet port 8 and an outlet port 9 of the blood positioned respectively at both ends of the blood channel and a pair of heat transfer thin tube headers 6, 7 forming flow chambers 14a, 14b, 15a, 15b that respectively surround both ends of the thin tube bundle and having an inlet port 6a and an outlet port 7a of the heat medium liquid. The thin tube bundle is divided into a plurality of thin tube bundle units 12a to 12c, and the heat transfer thin tube headers are configured so that the heat medium liquid passes through the plurality of the thin tube bundle units successively. Heat exchange efficiency is enhanced while the flow speed of the heat medium liquid flowing through the heat transfer thin tubes is increased to suppress the increase in volume of the blood channel.
