Iranian traditional houses is designed such that it provides all welfare facilities and comfort for members of family. With the advent of modernism in Iran, principles that are used to make building are set aside. Then western principles and standards determine the policy of Iranian architect. But in country like Japan whose architecture is close to Iranian architecture in terms of principles observance, it is observed that with arrival of modernism, they try to preserve the spirit and tradition of Japanese life in modern designs. This paper aims to study advent of modernism in Japan and Iran and how both countries face with this modern architecture, and why a country like Iran that has stronger principles and values and richer architecture more than Japan has lost its identity upon arrival of modernism and just has copied the modernism and cubism designs. It is important to see whether we can revive traditional spirit and values of the past in the modern design through recognizing Iranian traditional architecture. The method of study is analytical- descriptive one. The method to collect information and data is library method. Consequently, when we assess built modern houses in Japan, we observe that Japanese architecture absorb the modern architecture in its architecture and even when we look at the Japanese modern building we can call them Japanese building. But in Iranian architecture, we face a condition changing from introversion to extroversion and no trace of Iranian architecture’s attractive quality is observed.