To strictly and easily set the protruded quantity of a driver bit from a threadedly engaged quantity adjusting tool that threadedly engages a screw flush with a surface to be threadedly engaged such as floor and wall surfaces.

This adjusting tool is equipped with an adjusting tool main body 7: externally fitted and made mountable onto a driver bit 3, and a first setting means 22: for setting protruded quantity (e) of the driver bit 3 from the tip surface 33 of the main body 7 so that a screw 4 mounted on the tip of the driver bit 3 can be threadedly engaged flush with the surface to be threadedly engaged. The setting means 22 is equipped with a contact-stop part 23 for abutting to the shoulder part 5a of the driver bit 3 tip so as to regulate the movement to the base end side of the main body 7 to the driver bit 3.