An antibody molecule comprising as its constituent: (i) a heavy chain humanized variable region which is: (a) a mutant of the heavy chain humanized variable region of an antihuman epithelial cell growth factor receptor 1 antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp; or (b) a mutant of the heavy chain humanized variable region of said antibody 528, where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp and additionally Ser 55 is replaced by Thr, Lys, Arg, Asn or Gln, Lys 63 is replaced by Gln, Lys 65 is replaced by Gln, Asn 66 is replaced by Gln, Lys or Ser and/or Ala 97 is replaced by Thr; and (ii) a light chain humanized variable region which is: (a) a light chain humanized variable region of said antibody 528 which consists of an amino acid sequence represented by SEQ ID NO: 2; or (b) a mutant of the light chain humanized variable region of said antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:2, except that Lys 55 of 5L is replaced by Leu, Asp 58 of 5L is replaced by Arg and/or Phe 60 of 5L is replaced by Ser or Leu. (i) a heavy chain humanized variable region which is: (a) a mutant of the heavy chain humanized variable region of an antihuman epithelial cell growth factor receptor 1 antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp; or (b) a mutant of the heavy chain humanized variable region of said antibody 528, where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp and additionally Ser 55 is replaced by Thr, Lys, Arg, Asn or Gln, Lys 63 is replaced by Gln, Lys 65 is replaced by Gln, Asn 66 is replaced by Gln, Lys or Ser and/or Ala 97 is replaced by Thr; and (a) a mutant of the heavy chain humanized variable region of an antihuman epithelial cell growth factor receptor 1 antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp; or (b) a mutant of the heavy chain humanized variable region of said antibody 528, where the mutant consists of an amino acid sequence represented by SEQ ID NO:4, except that Tyr 52 of 5H is replaced by Trp and additionally Ser 55 is replaced by Thr, Lys, Arg, Asn or Gln, Lys 63 is replaced by Gln, Lys 65 is replaced by Gln, Asn 66 is replaced by Gln, Lys or Ser and/or Ala 97 is replaced by Thr; and (ii) a light chain humanized variable region which is: (a) a light chain humanized variable region of said antibody 528 which consists of an amino acid sequence represented by SEQ ID NO: 2; or (b) a mutant of the light chain humanized variable region of said antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:2, except that Lys 55 of 5L is replaced by Leu, Asp 58 of 5L is replaced by Arg and/or Phe 60 of 5L is replaced by Ser or Leu. (a) a light chain humanized variable region of said antibody 528 which consists of an amino acid sequence represented by SEQ ID NO: 2; or (b) a mutant of the light chain humanized variable region of said antibody 528 where the mutant consists of an amino acid sequence represented by SEQ ID NO:2, except that Lys 55 of 5L is replaced by Leu, Asp 58 of 5L is replaced by Arg and/or Phe 60 of 5L is replaced by Ser or Leu.