A thread-rolling flat die for a threaded fastener, includes a thread-rolling surface including at least a bite surface to which a workpiece of the threaded fastener is supplied, a finishing surface formed adjacent to the bite surface, and a roll-off surface formed adjacent to the finishing surface. The bite surface includes at least: a first partial bite surface having an inclination and a second partial bite surface formed continuously from the first partial bite surface and having an inclination. A length L1 along a thread-rolling direction in the first partial bite surface, a length L3 along the thread-rolling direction in the finishing surface, a length L4 along the thread-rolling direction in the roll-off surface, and a diameter of a processed portion of the workpiece of the threaded fastener have a relationship of L1>L3>L4> the diameter of the processed portion.