To provide a throw-away rotary cutting tool which facilitates replacement of throw-away tips, is high in repeated machining precision, and long in life.

A rear end of the throw-away tip 2 is formed of a taper surface 4protruding to a rear end at a location closer to an axis 3, an engaging surface protruding from the taper surface 4 and facing a tool reverse rotating direction at the time of cutting, and a rod portion 8 protruding from a protrusion end of the taper surface 4 toward a holder 1 and having a notch 7 for accommodating a fixing means 6 therein. Then the rear end of the throw-away chip is detachably mounted in the tip of the holder 1 having a recessed taper surface 9 recessed toward a proximal end at a location closer to the axis 3, an engagement bearing surface protruding from the recessed taper surface 9 and facing in a tool rotating direction at the time of cutting, a fitting hole 11 formed in a deep end of the recessed taper surface 9, and an insertion hole 12 for a fixing means 6, which is diagonally formed with respect to the shaft center 3, and becomes closer to the axis 3 as the hole extends from a distal end of the holder 1 to the proximal end of the same.