A bispecific antibody comprising humanized variable regions of the heavy chain and the light chain of an anti-human EGF receptor 1 antibody 528, and humanized variable regions of the heavy chain and the light chain of an anti-CD3 antibody OKT3, which is: a diabody-type bispecific antibody consisting of a first polypeptide comprising a humanized variable region of the light chain of an anti-human EGF receptor 1 antibody 528 and a humanized variable region of the heavy chain of an anti-CD3 antibody OKT3 in this order from its N-end to C-end; and a second polypeptide comprising a humanized variable region of the light chain of an anti-CD3 antibody OKT3 and a humanized variable region of the heavy chain of an anti-human EGF receptor 1 antibody 528 in this order from its N-end to C-end; or a humanized highly functional bispecific antibody having one of the following structures where the 5H, 5L, OH and OL regions are in the order specified from N-end to C-end: (i) -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)-; (ii) an antibody wherein a humanized diabody-type bispecific antibody consisting of two kinds of the single-chain polypeptides of and (OL5H) is bonded to two Fc regions of a human antibody via each hinge region through either of the two single-chain polypeptides; or (iii) an antibody wherein the single-chain polypeptide of -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)- is bonded to two Fc regions of a human antibody via each hinge region, wherein the 5L, 5H, OL and OH have an amino acid sequence represented by SEQ ID NOS: 2, 4, 6 and 8, respectively. a diabody-type bispecific antibody consisting of a first polypeptide comprising a humanized variable region of the light chain of an anti-human EGF receptor 1 antibody 528 and a humanized variable region of the heavy chain of an anti-CD3 antibody OKT3 in this order from its N-end to C-end; and a second polypeptide comprising a humanized variable region of the light chain of an anti-CD3 antibody OKT3 and a humanized variable region of the heavy chain of an anti-human EGF receptor 1 antibody 528 in this order from its N-end to C-end; or a humanized highly functional bispecific antibody having one of the following structures where the 5H, 5L, OH and OL regions are in the order specified from N-end to C-end: (i) -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)-; (ii) an antibody wherein a humanized diabody-type bispecific antibody consisting of two kinds of the single-chain polypeptides of and (OL5H) is bonded to two Fc regions of a human antibody via each hinge region through either of the two single-chain polypeptides; or (iii) an antibody wherein the single-chain polypeptide of -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)- is bonded to two Fc regions of a human antibody via each hinge region, (i) -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)-; (ii) an antibody wherein a humanized diabody-type bispecific antibody consisting of two kinds of the single-chain polypeptides of and (OL5H) is bonded to two Fc regions of a human antibody via each hinge region through either of the two single-chain polypeptides; or (iii) an antibody wherein the single-chain polypeptide of -(a peptide linker)-(OL5H) or (OL5H)-(a peptide linker)- is bonded to two Fc regions of a human antibody via each hinge region,