The tunnels of 55 national hyghway are constructed or under construction by the Ministry of Construction in mountainous Shikoku disrict which mainly consists of Paleozoic, Mesozic sedimentary and metamorphic rocks. The writer summerized geological conditions and construction records of these tunnels. There is distinct difference in selection of steel support type of tunnels in Paleozoic and Mesozoic rocks which will be caused by their geological conditions. It is shown that difficulties of construction, containing failures of portal, surface subsidence, caving and squeezing grounds are closely connected with geological feateres of tunnel sites in Shikoku.
