The present invention provides a method of improving iPS cell establishment efficiency, comprising contacting a protein involved in primitive streak (PrS) formation, preferably Foxh1, or a nucleic acid that encodes the same with a somatic cell in a nuclear reprogramming step. Also provided is a method of producing an iPS cell, comprising contacting the protein involved in PrS formation or a nucleic acid that encodes the same, and nuclear reprogramming substance(s) with a somatic cell.