The present invention discloses a fractionation device used for proteins and/or peptides, which has any of the following features:1) At least one portion of a substrate surface with which proteins or the like are made in contact has an amount of adsorption of bovine serum albumin of 50 ng/cm2 or less with respect to the substrate surface, when a bovine serum albumin solution is made in contact therewith.2) At least one portion of a substrate surface with which proteins or the like are made in contact has an amount of adsorption of human β2-microglobulin of 3 ng/cm2 or less with respect to the substrate surface, when a protein aqueous solution consisting of human β2-microglobulin and bovine serum albumin is made in contact with the substrate surface.3) The fractionation device is provided with: a means for supplying a solution containing proteins or the like； a means for separating proteins or the like from the solution； and a means for concentrating proteins or the like in the solution, and in the fractionation device, at least one portion of the substrate surface with which proteins or the like are made in contact is subj ected to a grafting process by using a hydrophilic polymer.By using the above-mentioned device, it becomes possible to reduce non-peculiar adsorption of protein onto the substrate, and consequently to easily provide a sample from which proteins having high-molecular weights have been removed, and which is advantageously used for an analysis.
