Bispecific antibody binding to her3 and cd3

The present invention relates to a bispecific antibody binding to HER3 and CD3, the antibody comprising a first polypeptide of SEQ ID NO: 1, a second polypeptide of SEQ ID NO: 2, a third polypeptide selected from the group consisting of SEQ ID NOS: 3 and 5, and a fourth polypeptide selected from the group consisting of SEQ ID NOS: 4 and 6, and showing excellent effects of engaging immune cells specifically with HER3-positive cells and inducing the growth suppression and death of HER3-positive cells, without causing side effects attributed to non-specific cytotoxicity.