Abstract: A thread forming device 10a is provided with a thread forming tool 32 for forming a thread portion 14 at a frame 12, a first motor 38 for controlling to rotate the thread forming tool 32, and a second motor 40 for controlling to extract and retract the thread forming tool 32. Further, the thread forming tool 32 is provided with a pilot hole forming portion 86 provided with a spiral groove 80b at a front end portion 80 in a taper shape, and a thread forming portion 84 constituted continuously to the pilot hole forming portion 86 and provided with a spiral groove 84b.