An indexable thread forming tap including: a body in a shaft shape; and a tip concentrically and detachably attached to a leading end portion of the body by screw-fastening and rotationally driven around an axial center along with the body for rolling of a female thread, the body being disposed with a screw hole concentrically to the axial center such that a screw shaft disposed on the tip concentrically to the axial center is screwed into the screw hole for the screw-fastening, a leading end surface of the screw shaft being pressed against a bottom surface of the screw hole into close contact with each other by the screw-fastening to integrally fix the tip to the body without the leading end of the body abutting on the tip, the body being disposed with a restraining hole concentrically to the axial center.