A method for producing an antibody, comprising introducing into a suspension CHO cell: (a) an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment, an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment, or (b) an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment, or (c) an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment, wherein each pair of transposon sequences are Toll nucleotide sequences or Tol2 nucleotide sequences; allowing a transposase to act upon the transposon sequences thereby integrating the gene fragments into a chromosome of the CHO cell to obtain a CHO cell which expresses the antibody; and suspension-culturing the CHO cell. (a) an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment, an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment, or (b) an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment, or (c) an expression vector which comprises a gene fragment comprising a DNA encoding a L chain of an antibody and a selectable marker gene and also comprises a pair of transposon sequences at both terminals of the gene fragment and an expression vector which comprises a gene fragment comprising a DNA encoding a H chain of an antibody and also comprises a pair of transposon sequences at both terminals of the gene fragment,