To provide a worm form-rolling device and a worm form-rolling method capable of accurately finishing a worm formed on a shaft by rough working.

A thread-rolling device 21 has a 1st roll die 23 and a 2nd roll die 24, and subjects a worm, which is beforehand formed by rough cutting on the outer peripheral surface of an armature shaft of a motor with a reduction mechanism, to form-rolling while putting the worm between these dies 23, 24. A support block 31 supporting the armature shaft freely rotatably and freely movably in its axial direction is energized by a spring 37 toward the side of the 1st roll die 23, and the armature shaft is pressed against the 1st roll die 23. When the 1st roll die 23 rotates while being pressed by the armature shaft and a shaft position sensor 44 detects that the armature shaft reaches a predetermined position in the axial direction, the 2nd roll die 24 is brought into contact with the armature shaft, and thread-rolling is started.