PURPOSE: To facilitate the control of the attitude of a caisson by setting a steel caisson of a double wall structure consisting of an outer wall, a radial inner wall, and a cutting blade into the ground while charging water ballast into a space between the outer and inner walls.

CONSTITUTION: A caisson 1 made of a steel material has a double wall structure consisting of outer walls 2 whose lower end are provided with a cutting blade 3 and a radial inner wall 4 whose lower end is positioned above the cutting blade 3. In setting and fixing the caisson 1, the caisson 1 is towed to a sea area to be set, positioned, and settled while charging water ballast into partitioned chambers 6 between the outer and inner walls 2 and 4 to control the attitude of the caisson. The cutting blade 3 is penetrated into the grounds 14 and 15, and then soil and sand are charged into the space 16 of the caisson 1. Thus, the attitude of the caisson 1 in the settlement and towing work can be easily controlled.