Abstract: Provided are a nut processing cutting tool configured to form an internal thread at the inner peripheral surface of a nut of a sliding screw device with high accuracy, high strength, and low cost, and a nut processing method therefor. A nut processing cutting tool (1) includes a cylindrical cutter (4) and a recessed groove (3) formed in a helical pattern at the outer peripheral surface (2) of the cutter (4). The recessed groove (3) forms, by cutting, a ridge portion (13) of an internal thread (11) corresponding to the shape of the recessed groove (3) at the inner peripheral surface of a nut (10). Thus, the internal thread (11) can be formed at the inner peripheral surface of the nut (10) of the sliding screw device (100) with high accuracy, high strength, and low cost.