A tumor-specific cytosol-internalized RAS-inhibiting antibody, in which modified heavy-chain variable region and a light-chain variable region are combined, according to the present disclosure facilitates development into a therapeutic drug due to a high production yield, and can effectively suppress mutant RAS by means of tumor-specific internalization into the cytosol, and thus effective anti-cancer activity can be expected as a stand-alone drug or in combination treatment with existing medicine.