Provided is a thread mill that can reduce tilting of an internal thread to be machined, thus increasing the tool life. A thread mill includes a plurality of thread cutting edges that are circumferentially spaced apart on a front end side of an outer circumference of a tool body, and a plurality of end cutting edges formed at the front end of the tool body. A functional cutting edge portion that cuts a workpiece, and a non-functional cutting edge portion that is relieved toward an axial shank end relative to a trajectory of the functional cutting edge portion when the tool body is caused to make one rotation about an axis are formed on the plurality of end cutting edges.