Method for the preparation of a nucleic acid library

[Subject] Offer of the method for producing the nucleic acid library containing two or more elements. [Solution means] Each element includes the arrangement of the 2nd nucleotide stretch that has different arrangement between elements, including the 1st [which has the same arrangement], and 3rd nucleotide stretches. The 1st ligation output is formed from the 1st oligonucleotide and the 1st oligonucleotide library, and it cuts by an IIS type restriction enzyme. The shortened oligonucleotide after cutting is removed, the 2nd ligation output is formed from the 1st ligation output after cutting, and the 2nd oligonucleotide library, and it cuts by an IIS type restriction enzyme. The shortened oligonucleotide after cutting is removed, the 3rd ligation output is formed from the 2nd ligation output after cutting, and the 4th oligonucleotide, and it cuts by an IIS type restriction enzyme. The shortened oligonucleotide after cutting is removed. [Selection figure] Fig. 1 (1)