To take the sunlight in a basement and a north side room by excavating an empty moat in front of a basement part, inclining its wall surface, and imparting the light to an underground part by reflecting the sunlight or emitting the light by its surface.

An earth retaining wall 3 is arranged in an empty moat of a building 1 by concrete, and it is inclined, and its wall surface 4 is also painted with, for example, white paint 5, and is formed as a reflecting surface of the light, and the light 7 of the sun 6 is reflected by a surface of the white paint 5, and can also be taken in a basement B1 of the building 1. The earth retaining wall 3 may be comparatively low strength, and a material not architectural structure material can be used, and waste resources can be utilized thereby, and a work cost can also be reduced. When an inclination of the earth retaining wall 3 is set to, for example, upward 45 degrees, the light 7 of the sun 6 reflects so as to be made effectively incident on a window 8 of the basement B1, and is also made directly incident on the window 8, and the basement B1 can be brightened further. It is also formed as a surface by mixing a phosphor and a light accumulating body in cement of the wall surface 4, and the absorbed light may be emitted.