GEH house is located on the main street of Kodaira-City, Tokyo. Our challenge was to design a wide comfortable space on which enough sunlight pours, in the small site surrounded by tall buildings but west side. By placing the main bedroom and the water closet in the first floor, we obtained the maximal volume for the living and kitchen space on the second floor within the setback regulation from site boundary. The "box beam", which includes the children's room and free space inside, enables a column-less wide space. From top of the southern elevation over the box, the room is illuminated by full of natural sunlight.