PROBLEM TO BE SOLVED: To provide polypeptides which satisfy both of high functionality of the functional domain and high recognition specificity to DNA sequence, exert desired function with a high probability and safety, and are prepared by a simple method.SOLUTION: The invention provides: an artificial nuclease comprising a DNA binding domain and a functional domain linked with a polypeptide of 35-55 amino acids, where four DNA binding modules each of which has a different set of two amino acids at certain positions of the module are repeated forming a pattern in the DNA binding domain; a vector for expressing the artificial nuclease; a vector library for preparing the vector; and a vector set for preparing the vector library.SELECTED DRAWING: None