PURPOSE: To enable caisson to be securely and easily launched by fabricating caisson on a flat deck of floating vessel, and by slanting the vessel after fabricated caisson is transported together with the vessel to any suitable launching place.

CONSTITUTION: Floating vessel 1 provided with ballast tanks No.1W10 symmetrically divided by partitions is positioned on mount 2 formed by broken stones accumulated in a suitable sea coast 15 and stably seated on buffer material 5 such as used tires placed on the mount 2 by filling any number of tanks with water as required. Caisson 3 is fabricated on thin sand layer laid on flat deck of the vessel 1. Upon completion of caisson 3, tanks of vessel 1 is emptied as required so as to allow vessel 1 to be floated on water, and every openings, if any, are securely closed by watertight closures 6. Floating vessel 1 is thereafter towed to launching place, and securely anchored by any suitable anchor means 8. Tanks No.3 and No.8 of vessel 1 are filled with water in order that the flat deck of vessel is brought at a level higher than water surface by nearly 50cm. Finally, caisson 3 is launched from vessel 1 which is slanted to portside, for example, owing to portside tanks No.2 and No.4 filled with water.