A monoclonal antibody that binds to a GPR49 protein comprising the amino acid sequence of SEQ ID NO:1, wherein the antibody has cytotoxic activity against cells expressing the GPR49 protein, wherein the antibody binds to a 40kDa C-terminal fragment of the GPR49 protein, wherein the antibody comprises a human constant region, and wherein the antibody is selected from the group consisting of to below: an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 5 as CDR1, the amino acid sequence of SEQ ID NO: 6 as CDR2, and the amino acid sequence of SEQ ID NO: 7 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 10 as CDR1, the amino acid sequence of SEQ ID NO: 11 as CDR2, and the amino acid sequence of SEQ ID NO: 12 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 15 as CDR1, the amino acid sequence of SEQ ID NO: 16 as CDR2, and the amino acid sequence of SEQ ID NO: 17 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 20 as CDR1, the amino acid sequence of SEQ ID NO: 21 as CDR2, and the amino acid sequence of SEQ ID NO: 22 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 25 as CDR1, the amino acid sequence of SEQ ID NO: 26 as CDR2, and the amino acid sequence of SEQ ID NO: 27 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 30 as CDR1, the amino acid sequence of SEQ ID NO: 31 as CDR2, and the amino acid sequence of SEQ ID NO: 32 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 35 as CDR1, the amino acid sequence of SEQ ID NO: 36 as CDR2, and the amino acid sequence of SEQ ID NO: 37 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 40 as CDR1, the amino acid sequence of SEQ ID NO: 41 as CDR2, and the amino acid sequence of SEQ ID NO: 42 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 45 as CDR1, the amino acid sequence of SEQ ID NO: 46 as CDR2, and the amino acid sequence of SEQ ID NO: 47 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 50 as CDR1, the amino acid sequence of SEQ ID NO: 51 as CDR2, and the amino acid sequence of SEQ ID NO: 52 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 66 as CDR1, the amino acid sequence of SEQ ID NO: 67 as CDR2, and the amino acid sequence of SEQ ID NO: 68 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 71 as CDR1, the amino acid sequence of SEQ ID NO: 72 as CDR2, and the amino acid sequence of SEQ ID NO: 73 as CDR3; an antibody that can block binding of the antibody of any one of to to the GPR49 protein by at least 50% when detected by a cross-blocking assay; and an antibody that binds to the same epitope as the GPR49 protein epitope bound by the antibody of any of to, wherein the GPR49 protein epitope exists in the amino acids from positions 495 to 537 of the GPR49 protein. an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 5 as CDR1, the amino acid sequence of SEQ ID NO: 6 as CDR2, and the amino acid sequence of SEQ ID NO: 7 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 10 as CDR1, the amino acid sequence of SEQ ID NO: 11 as CDR2, and the amino acid sequence of SEQ ID NO: 12 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 15 as CDR1, the amino acid sequence of SEQ ID NO: 16 as CDR2, and the amino acid sequence of SEQ ID NO: 17 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 20 as CDR1, the amino acid sequence of SEQ ID NO: 21 as CDR2, and the amino acid sequence of SEQ ID NO: 22 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 25 as CDR1, the amino acid sequence of SEQ ID NO: 26 as CDR2, and the amino acid sequence of SEQ ID NO: 27 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 30 as CDR1, the amino acid sequence of SEQ ID NO: 31 as CDR2, and the amino acid sequence of SEQ ID NO: 32 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 35 as CDR1, the amino acid sequence of SEQ ID NO: 36 as CDR2, and the amino acid sequence of SEQ ID NO: 37 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 40 as CDR1, the amino acid sequence of SEQ ID NO: 41 as CDR2, and the amino acid sequence of SEQ ID NO: 42 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 45 as CDR1, the amino acid sequence of SEQ ID NO: 46 as CDR2, and the amino acid sequence of SEQ ID NO: 47 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 50 as CDR1, the amino acid sequence of SEQ ID NO: 51 as CDR2, and the amino acid sequence of SEQ ID NO: 52 as CDR3; an antibody comprising an H chain having the amino acid sequence of SEQ ID NO: 66 as CDR1, the amino acid sequence of SEQ ID NO: 67 as CDR2, and the amino acid sequence of SEQ ID NO: 68 as CDR3, and comprising an L chain having the amino acid sequence of SEQ ID NO: 71 as CDR1, the amino acid sequence of SEQ ID NO: 72 as CDR2, and the amino acid sequence of SEQ ID NO: 73 as CDR3; an antibody that can block binding of the antibody of any one of to to the GPR49 protein by at least 50% when detected by a cross-blocking assay; and an antibody that binds to the same epitope as the GPR49 protein epitope bound by the antibody of any of to, wherein the GPR49 protein epitope exists in the amino acids from positions 495 to 537 of the GPR49 protein.