Provided is a method of improving the efficiency of iPS cell establishment, comprising bringing one or more factors selected from the group consisting of proteins belonging to cyclin D family and nucleic acids that encode the same into contact with a somatic cell, in the step of nuclear reprogramming of the somatic cell. Also provided are a method of producing an iPS cell comprising the step of bringing the factor(s) and nuclear reprogramming substance(s) into contact with a somatic cell, an iPS cell comprising a nucleic acid that encodes a protein belonging to cyclin D family that can be obtained by the method of producing an iPS cell, and a method of somatic cell production by forcing the iPS cell to differentiate.