PURPOSE: To save labor for construction of a provisional wall surface, perform construction economically, and widen the degree of design freedom.

CONSTITUTION: An injection bag 10 in which a laydown part 11a is formed in a provisional wall surface constructing position X2, is laid in such an arrangement that the laydown part is positioned on the banking forming part MS side. Mortar 9 is injected into the laid bag so that a block 5 is formed. One banking 2 is formed in the form that laydown part is buried on the nabking forming part side of the block formed. These first, second, and third processes are repeated so that a plurality of bankings are piled up to the constructing height H in the banking forming part, and meantime a sheet-form reinforcing material 6 is laid selectively between the laminated bankings. Thus provisional wall surface 1 is completed.