Low-seated chairs for tatami mats that are characteristic of Japanese-style interior appeared after late 1940s. This article focuses on the ambivalence between Western lifestyles and Japanese lifestyles by tracing the comments of designers, critics, magazines, and so forth to clarify a background of them. The introduction of chairs in Japan was actually involved, by definition, in a dichotomy between sitting on the floor and in chairs, which therefore was far from the domestic practicality of lifestyles among the public. Then we have to observe the two points for the introduction of chairs to break through this rigid situation: (1) how did the public establish definition of chairs outside the Westernization? This article grasps the fact that the artisans and early designers accumulated their experience of producing chairs from scratch, through trial and error. (2) How did the relation between sitting on the floor and in chairs break out of the dichotomy, through ambivalence? This article focuses on the fact that the public enjoyed the physical relaxation offered by the mix of sitting on the floor and in chairs. This constituted the domestic practicality of chairs for the Japanese. Therefore, such experiences of making and using chairs can be summarized as the awakening of a universe in the distance between the floor and the seat-height of Western chairs. It was a new frontier for Japanese designers, and low-seated chairs were born in this space. This article concludes that it marked the transition from Westernization to Japanese modern design.