To surely mount a wall panel receiving member on the correct level without being affected by the condition of an upper surface of a concrete floor.

A long support base 3 is arranged along the line of each wall of a unit room A to be formed, and a lower part of the long support base 3 is embedded in a concrete floor 4. An upper part of the long support base 3 is projected upward from the concrete floor 4, and a wall panel receiving member 2 is installed on the upper surface part of the long support base 3. A wall panel 1 forming a wall of the unit room A is installed on the wall panel receiving member 2.