A substrate for biochips which has a high probe loading amounts and a uniform immobilization density, and which further has a high detection sensitivity and a high reproducibility by preventing a non-specific adsorption of proteins, when used as a substrate for biochips for immobilizing probes composed of biologically relevant substances such as proteins and nucleic acids, is disclosed. Amino groups can be bound to the surface of the substrate uniformly, at a high density and stably by covalently immobilizing an amino group-containing polymer on the surface of the substrate. The probe immobilization rate is high and immobilizing density was uniform by immobilizing a probe composed of a biologically relevant substance such as a protein or nucleic acid by utilizing the amino groups. Further, detection sensitivity and reproducibility are high by inhibiting non-specific adsorption of proteins.