PURPOSE: To improve the certainty of regulating operation in an automatic regulating machine which performs automatic regulating by engaging a driver bit with a pre-set resistor.

CONSTITUTION: A taper part 7a is formed in a bit holder 7. A taper accepting surface 4a corresponding with the taper part 7a is formed in a positioning board 4. In the state that the taper part 7a is bonded to the taper accepting surface 4a, the whole part of a retaining stand 2 is made to descend, and a driver bit 9 is made to engage with a pre-set resistor 10. After that, the positioning board 4 is moved to set the bit holder 7, i.e., a driver bit 9 in a free state. In this state, the torque of a motor 6 is transferred to the driver bit 9 via a flexible coupling 12, thereby automatically regulating the pre-set resistor 10.