This nano-polycrystalline diamond (1) comprises carbon, a non-carbon foreign element (3) added so as to be dispersed throughout the carbon at an atomic level, and unavoidable impurities. Said polycrystalline diamond has a crystal grain size of 500 nm or less and can be fabricated by subjecting graphite, to which a non-carbon foreign element has been added so as to become dispersed throughout the carbon at an atomic level, to a heat treatment in a high-pressure press device.