An object is to provide a Tol1 element transposase and a use thereof. Provided is a Tol1 element transposase containing (a) a protein having the amino acid sequence of SEQ ID No: 1 or (b) a protein having an amino acid sequence homologous to the amino acid sequence of SEQ ID NO: 1 and having an enzymatic activity for transferring Tol1 element. Further, provided is a polynucleotide encoding the transposase and an expression construct containing the polynucleotide therein. The present invention also provides a DNA introduction system including (a) a donor factor having such a structure that a desired DNA is inserted in a transposase gene-defected Tol1 element and (b) a helper factor containing the transposase or the polynucleotide.