This paper focuses on Mamoru Yamada's architectural design of Hiroshima Post Hospital. As the first series of his design for the hospital, it represented the latest hospital layout including a definite design on the zoning and a movable outline function. Especially when we refer to the layout of consultation rooms. With the internal medicine room as the center, the surgery, ophthalmology, and x-ray room were allocated according to the American 'History Corridor' design. With the sunroof, the technique of catching the sunlight had been used. In order to get enough sunlight for the corridor, in between the border of each room, parapet is used as the upper part of the roof as well as the well-ventilated window. This type of architectural design concept marks the beginning of the modern rationalistic architectural in the modern Japan. In addition, it has a profound impact on the latest rationalistic work such as the architectural design of Tokyo Post Hospital.