PURPOSE: To efficiently and safely build a block layer during building of an undersea structure with the use of a pile driving coupling block process.

CONSTITUTION: A panel point device 31 in which a panel point block is suspended from a pile head 31c having its upper part fixed thereto with second steel rods 35 coupled thereto with extension steel rods 5 is set up to a pile 30 having driven in the sea bottom, and a plurality of blocks 32a are stacked on the panel point block. A fixture 36 is built and fixed on the upper surface of the block layer through which the second steel rods 35 pierce, and a cylindrical caisson 6 having its upper part exposed from the sea surface is set surrounding around the fixture 36. More than one of extension rods 5 are stretched on the caisson 6 so that the inside of the caisson 6 becomes water-tight, and then water is discharged from the inside of the caisson 6. Then nuts 12 are tightened onto the second steel rods 35 while the water-tight condition is held so as the second steel rods 35 are stretched together with the extension rods 5, and after the second steel rods 35 are coupled to the fixture 36 by means of the nuts 12, the caisson 6, the extension rods 5 and the like are removed.