It is an object of the present invention to provide a biosensor with an improved recovery yield of a test substance interacting with a physiologically active substance. The present invention provides a biosensor having a flow channel formed on a substrate, which is composed of a detection surface for detecting the interaction of a physiologically active substance with a test substance and a non-detection surface that does not detect said interaction, wherein the detection surface and non-detection surface are modified in such a way that the physiologically active substance can be immobilized thereon.