The purpose of this study is to clarify the spatial composition of Japanese contemporary houses in the way of making "depth" through the relationship between a principal room and a building lot. The principal room is characterized by several aspects, such as its position in a lot, the way to the principal room from the street and the view from its window. It turns out fourteen types of Japanese contemporary houses. According to these characteristics, the property of the 'depth' that have been given in Japanese traditional houses gets growing weaker, and its decline is found especially after the 1980s.