"In this paper a transition of urban space in Tokyo is reported from theviewpoint of urban design paradigm. The sample for survey is Marunouchi,a central business district in Tokyo, which has been developed during thiscentury-long Japanese rapid modernization. The author characterizes thetransition by three periods, e.g. befor World Var 2, after the war, and veryrecently. Before the war the district was developed after the model of vari-ous Western styles. So it was composed of four different types of block indi-cating the development stages, and there was an urban design code to har-monize those types. After the war most old buildings were reconstructedfunctionally and the space of the district became homogeneous. Very recent-ly under the circumstance of another large redevelopment wave, a new ur-ban design paradigm and a code are being discussed to conserve the history ofmodern eras in townscape for the coming century.The development of Marunouchi district, about 5Oha facing the ImperialPalace, started in 1894 when the first building was built on the vacant land.Since then building styles had changed one after another as Japan importedbuilding styles from Western countries to build a modern city rapidly.First, red-brick buildings were built on both sides of a street after themodel of Lombart street in London. It was called "one block London". Next,early modern style buildings stood around the block. Sone of them had a tasteof art nouveau or secession style. After the completion of Tokyo station in1914 large modern buildings appeared near the station. Their style or con-struction method was imported fromthe United Sates. Along the moat of Pal-ace grand or florid, rather classic style buildings were located- So, beforethe war the district was composed of four types of townscape which indicatedthe development stage and location. Buildings standing at the boundarycrossings of those types were designed strikingly as gates. This is an urbandesign code to harmonize the connections among the diffrent townscape ele-ments without losing their identities. But after the war when Japanese economy grew at a fast rate, many buildings were demolished and newlyconstcructed in the international style. No historical attention was paid tothe designs of new buildings. Because ofthe design and height standardization,the townscape was in good order but homogeneous. Since the first highrisebuilding in Marunouchi was constructed in 1971 after a great aesthetic dis-pute, there has been no urban design paradigm or code which characterizesthe district. Very shortge of office space and astronomical rise in land pricesin Tokyo. Against such plans as demolition of Tokyo station or "MarunouchiManhattan Plan", citizens' movement has arisen demanding forthe save ofprewar, citizens' movement has arisen demanding for the save of prewarbuildings which remind them ofthe Japanese modernization history. Now,planners, architects, developers, and citizens are debating how to conservethe history in urban space under the economical situation and how to har-monize the elements that are different greatly in design and scale."