Abstract: A device for controlling the drilling direction of drills includes a cylinder-type housing 6, a first ring-formed component 11 which is located on an inner peripheral surface that is eccentric with respect to the cylinder-type housing 6, a second ring-formed component 12 which is located on the inner peripheral surface that is eccentric with respect to the circular inner surface of the first ring-formed component 11, and hollow-type harmonized reduction gears 13,14 which rotate the first and second ring-formed components 11,12 relatively around their respective centers. A resolver is positioned between the first and second ring-formed components 11,12 and the hollow-type harmonized reduction gears 13,14 to detect the rotating angular position of the first and second ring-formed components 11,12. A fulcrum bearing 8 of the rotating shaft 2 is located at a midpoint between the drill bit and the first and second ring formed components 11,12.