To provide a long life tool improving flank wearing resistance and chipping resistance without large worsening cutting resistance and finish surface roughness, by constituting a grain size by a diamond particle of prescribed dimension or less, and forming rake face roughness in a prescribed range.

In a sintered diamond cutting tool, to a 7 to 9μm diamond grain size, a flank wearing width and chipping width are decreased when the grain size is decreased, a tool life is extended, but when the grain size is further decreased, the chipping width is decreased, but the flank wearing width is increased. Accordingly, in a range extending a tool life by considering flank wear resistance and chipping resistance of the tool, the diamond grain size is limited to 6μm or less. When rake face roughness is made less than 1μmRmax. the flank wearing width is extremely increased, so as to limit a lower limit to 1μmRmax, in a 1 to 10μmRmax. In this range, cutting resistance and finish surface roughness are increased, but in a permissible range.