The present inventors produced a heterodimerized polypeptide having an Fc region formed from two polypeptides with different amino acid sequences (a first polypeptide and a second polypeptide), and succeeded in producing a heterodimerized polypeptide containing an Fc region with improved function compared to that of a homodimer in which the Fc region is composed of only the first polypeptide or the second polypeptide by conventional technology.