INTRODUCTION In order to realize successful fine and precise EDM, it is important to minimize the wear of the electrode under the condition of very small pulse duration. To cope with this issue, the authors focused attention on the electrically conductive CVD diamond (EC-CVD diamond here after) having very high thermal conductivity, and have already shown that an extremely low wear machining could be realized by using the ECCVD diamond as an electrode [1, 2]. Subsequently, the authors proposed the use of PCD (polycrystalline diamond) material having adequately high thermal conductivity instead of expensive EC-CVD diamond, and have shown that the PCD also has superior wear resistance in EDM on die steel (SKD11 in JIS) similar to the EC-CVD diamond electrode [3].