CBN is used as a cutting tool material of the hardened steel. Recently, the cutting speed by cBN tool shows the tendency to rise around Europe. In addition, the improvement of the quality of the surface of the work after cutting processing by cBN tool is requested. We made the cBN sintered compact of fine grain and carried out the cutting test of the hardened steel. As a result, the cBN compact of fine grain showed an excellent cutting performance in a high-speed cutting of the hardened steel.