Cable made by bundling fine high tensile strength materials has flexibility and the strength to weight ratio is high. Also a great advantages of cable is that there is no limit to the length of members from a manufacture and a transportation view point. When applying cables to structures, it is effective to use the "middle clamp jointing method" in order to make the best economical use of both the properties of cables and their advantages over other materials. This method, in which other members are connected to the middle part of a cable, has the most distinctive characteristic that a single long cable can be used continuously without being cut at the clamping part unless absolutely necessary. This paper proposes a design method for a metal fittings for the cable structures by carrying out both experiments and analyses on the following items. (1) Principal factors for the design of metal fittings used for the middle clamp jointing. (2) A method for establishing an appropriate safety factors for the metal fittings of cable.