In Japan there exists a strong demand for mechanical excavation for tunnelling bacause the blasting method which produces much vibra- tions and noises is restricted in its applica- tion due to the fact that there can be many cases where tunnelling sites are located ad- jacent to residencial areas as a result of Japan's being a thickly inhabited country. Pressing demands for and deep interest in the mechanical excavation method have been shown by the circles concerned with reasons that it produces smooth cutting surface and causes less overcutting of profile as a result of the diffusion of NATM (New Austrian Tunnel- ling Method) in the recent years. This has caused a strong desire of the users to apply the conventional mechanical excavation method that has been used mainly for soft rock cutting also to the field of hard rock cutting. In order to meet such needs of the tunnel- ling industry, further research and development have been continued to have successfully real- ized the Boomtype Tunnelling Machine for Hard Rock.