PURPOSE: To enable conveying of a large structure of weight exceeding the hoisting capacity of a crane without using a crane of larger hoisting capacity in a method of conveying out the structure by carrying it on a float as built in a dock.

CONSTITUTION: Blocks 2 are disposed on the bottom surface 1 of a dock. After a surface plate 3 is carried on the blocks 2 as a foundation for installing a large structure at field, the structure P is installed on the plate 3 with necessary pipes and devices. Rollers 5 are slid under the plate 3 to convey in an auxiliary tank 4, which is then mounted under the plate 3. Then, sea water is introduced into the dock to hoist the structure P together with the plate 3 by using a cable 6 and utilizing buoyancy of a tank 4 to be moved to the place where bases 7 and towing tanks 8 are prepared. The structure P is temporarily carried on the bases 7. Then, the tanks 8 are installed under the plate 3 to float the structure P, which is thus towed to the place to be built.