A method of determining an amino acid sequence of a polypeptide that binds to a target molecule or a base sequence of a nucleic acid encoding the polypeptide comprising: a panning step for bringing a library constructed by a display method capable of associating polypeptides with nucleic acids encoding the polypeptides into contact with the target molecule, followed by incubation to obtain a polypeptide group that binds to the target molecule; a sequencing step of the following (a) or (b): (a) a sequencing step for analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; or (b) a sequencing step for determining an amino acid sequence based on a base sequence obtained by analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; a scoring step comprising evaluating and scoring, based on the results of the sequencing step, how much each base sequence or amino acid sequence is enriched by the panning step; and a step comprising selecting a polypeptide with a high score, wherein the amino acid sequence of the selected polypeptide is determined to be the amino acid sequence of a polypeptide that binds to the target molecule, or wherein the base sequence of the nucleic acid encoding the selected polypeptide is determined to be the base sequence of a nucleic acid encoding a polypeptide that binds to the target molecule. a panning step for bringing a library constructed by a display method capable of associating polypeptides with nucleic acids encoding the polypeptides into contact with the target molecule, followed by incubation to obtain a polypeptide group that binds to the target molecule; a sequencing step of the following (a) or (b): (a) a sequencing step for analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; or (b) a sequencing step for determining an amino acid sequence based on a base sequence obtained by analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; (a) a sequencing step for analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; or (b) a sequencing step for determining an amino acid sequence based on a base sequence obtained by analyzing a base sequence of a nucleic acid encoding all the polypeptides belonging to the polypeptide group of the library before the panning step and the polypeptide group of the library after the panning step by a next-generation sequencer; a scoring step comprising evaluating and scoring, based on the results of the sequencing step, how much each base sequence or amino acid sequence is enriched by the panning step; and a step comprising selecting a polypeptide with a high score, wherein the amino acid sequence of the selected polypeptide is determined to be the amino acid sequence of a polypeptide that binds to the target molecule, or wherein the base sequence of the nucleic acid encoding the selected polypeptide is determined to be the base sequence of a nucleic acid encoding a polypeptide that binds to the target molecule.