A main object of the invention is to provide a polymer compound for medicine which has an excellent capability of fixing a biologically active substance and has such chemical/physical stability that the compound is less dissolved or deteriorated in a washing step, in particular, which can be suitably applied to a plastic substrate surface.The invention provides a polymer compound for medical material which is a polymer comprising repeating units derived from an ethylenically unsaturated polymerizable monomer (a) having a functional group for fixing a biologically active substance, wherein the polymer has a reactive functional group on at least one terminal side thereof, and a biochip substrate wherein a layer containing the polymer compound is formed on a substrate surface, thereby attaining the object.