This office is built on a site with an alley-shaped entrance and pocket at the rear. Generally in the case of an alley-shaped site, buildings are positioned on the pocket at the rear of the site, however in this case we positioned the building on the alley-shaped side due to demand for allowing space for parking at the rear and visibility from the road front. Therefore, apart from the entrance, the whole site is used for vehicles and the office function is positioned in the box at the top of the site. The T-shaped box culvert is divided into a slender office and guest room. The natural light and air flowing through the opening at the edge of the box enables realization of an office environment not dependent on air conditioning and lighting.