To quickly perform execution by assembling a wall panel on a lower beam disposed on an excavation bottom, and placing pillar board concrete after an upper beam is attached to the upper part of the wall panel.

Ground is excavated together with earth retaining work, and the lower beam 4 of a basement wall body is disposed on an excavation bottom 11. Next, a plurality of wall panels 5, 6 are assembled along the lower beam 4 on the lower beam 4. Next, an upper beam 9 is provided on the upper end of the wall panels 5, 6, the upper beam 9 and the wall panels 5, 6 are connected by a bolt, after the upper beams 9 are mutually connected, a space between the wall panels 5, 6 and the upper beam 9 is filled with mortar to set the basement wall body. A base beam 20 is connected to the upper beam 9 of the basement wall body by a bolt to connect the base beams 20 to each other. Furthermore, after pillar board concrete is placed in a space part surrounded by the lower part of the wall panels 5, 6 of the basement wall body, an earth retaining wall is removed to bury the circumference of a basement casing. Thereby execution can be quickly performed.