Abstract: Provided is a novel therapeutic agent specific for a malignant tumor expressing MHC class II. The present invention provides an antibody recognizing a protein constituting MHC class II expressed on a malignant tumor, the antibody comprising at least one selected from heavy chain CDR1 (amino acid sequence represented by positions 49 to 54 of SEQ ID NO: 54), heavy chain CDR2 (amino acid sequence represented by positions 69 to 84 of SEQ ID NO: 54), heavy chain CDR3 (amino acid sequence represented by positions 117 to 128 of SEQ ID NO: 54), light chain CDR1 (amino acid sequence represented by positions 46 to 55 of SEQ ID NO: 56), light chain CDR2 (amino acid sequence represented by positions 71 to 77 of SEQ ID NO: 56), and light chain CDR3 (amino acid sequence represented by positions 100 to 108 of SEQ ID NO: 56).