There are provided sufficiently strong, hard, and heat resistant, dense and homogenous polycrystalline diamond applicable to cutting tools, dressers, dies and other working tools and excavation bits and the like, and a cutting tool having a cutting edge of the polycrystalline diamond. The polycrystalline diamond is formed substantially only of diamond formed using a composition of material containing a non diamond type carbon material, the composition of material being converted directly into diamond and sintered at ultra high pressure and ultra high temperature without aid of a sintering aid or a catalyst, and has a mixed microstructure having a fine crystal grain of diamond having a maximal grain size of at most 100 nm and an average grain size of at most 50 nm and a coarse crystal grain of diamond in the form of one of a platelet and a granule having a grain size of at least 50 nm and at most 10,000 nm.