The present invention relates to a cutting tool, especially the cutting tool having a head segment releasably attached to a shank segment. According to one aspect of this invention there is provided a cutting tool comprising: (i) a head segment rotatable around an axis thereof and a forward end portion having at least one cutting-insert receiving seat and a rearward end portion; (ii) a shank segment rotatable around an axis thereof having a forward end portion adapted to be coaxially joined with the rearward end of the head segment and a rearward end portion adapted to be fixedly secured to a machine spindle; (iii) an engaging hole coaxially formed on one of the above segments, which is provided with at least two internal threads communicating between the hole and the external surroundings through a peripheral surface of the segment; (iv) an engaging projection coaxially formed on other one of the segments and engagingly fitted into the hole; and (v) clamp screws respectively threaded through each internal thread, in which bottom ends of the clamp screws are contacted with a surface of the engaging projection.