The purpose of this study is to clarify the adhesion mechanism in cutting process on the difficult-to-machine material such as Ni-base alloys like Inconel 718, Inconel 600 and so on. For the elucidation of the adhesion mechanism, it seems to be important to know the reaction which is generated at the interface between cutting tool and material. However, it is difficult that the reactive phenomenon is observed in detail because the region where cutting tool contacts the material in cutting process is very small. Then, the friction welding test between cutting tool material, K10 (8mm diameter) and material was carried out. The reactive phenomenon between cutting tool and material in cutting process was analogized by the observation of the interface of friction welded joint. In addition, 4 point bending test at high temperature was carried out for diffusion bonding joint between K10 and material at 1373K. From analyzing fracture strength and rupture position, the strength of the bonded interface between K10 and material was examined. As a result of the friction welding test, Ni-base alloys and K10 were bonded together only for the friction time of 0.4s. Friction welding of Inconel 718 was easy to be done in comparison with Inconel 600 and pure Ni. In either material, the reaction layer was not observed in the interface of friction welding. On the other hand, the width of the reaction layer increased with the increase in the bonding time in the interface of the diffusion bonding joint. The growth of the reaction layer was the biggest in Inconel 718. This reaction phase was the η phase. High-temperature bending strength of the diffusion bonding joint in Inconel 718 and Inconel 600 was bigger than that in pure Ni. From the above experimental result, the reason why Inconel 718 and Inconel 600 are easy to adhere to cutting tool comparing with pure Ni was seemed to be that these materials were easy to react with cutting tool and bonding strength between these materials and cutting tool were high.