Abstract: A controlled directional drilling tool is disclosed which comprises a drilling unit consisting of a drilling head incorporating therein a rotary drill bit and bit-driving means and a drilling rod having said drilling head connected freely flexibly to the leading end thereof, a pair of cylinder means adapted to be operated by means of compressed air and a pair of direction-controlling rollers adapted so as to be caused, by the operation of said cylinder means, to protrude at mutually staggered positions from the opposite lateral sides of the drilling unit, said pair of cylinder means and said pair of direction-controlling rollers both provided to the drilling head of said drilling unit, whereby the direction in which the drilling is being made by said drilling head is changed as required by adjusting the protrusion of said pair of rollers.