PURPOSE: To execute most of the processes on the ground by mounting a roof above a bottom board and forming the peripheral wall in such a way that a peripheral wall board is spirally wound up from the bottom of the roof.

CONSTITUTION: The bottom part 1 of a tank is assembled and located on the installation side of a tank. A plurality of temporary frames 2 are placed at certain intervals along the periphery of the bottom board 1 and top angles 3 making up a roof are assembled. After roof girders 4 are put on the top angles 3 and assembled radially at certain intervals, roof board 5 are mounted, thus completing the assembly of a roof 6. After the roof 6 is assembled, a peripheral wall board 7 is spirally wound from the bottom of the roof 6 to gradually forming a peripheral wall 8 and at the same time, the peripheral wall 8 is turned and moved following the peripheral wall forming trace, whereby forming a peripheral wall 8 of the specified height between the roof 6 and the bottom board 1.