To realize space development and utilization, low cost space transportation system should be developed. However, if we concentrate only on development of space transportation system, the cost for development of it becomes quite high because the number of space transportation systems will be limited in small number. If HST (Hypersonic Transport), which flies over oceans and continentals, and lower stage of TSTO have similar aerodynamic characteristics, we could reduce the development cost significantly. The present paper proposes shared design of hypersonic vehicle in order to reduce development cost and manufacturing cost of HST and lower stage of TSTO. In the present paper conceptual design has been conducted both for HST and lower stage of TSTO.