PURPOSE: To exactly perform the leveling work of rubble-mound by mechanical forces by a method in which the level at the lower end of a seabed rubble mound leveler can be automatically adjusted to a reference level by the laser beam of a lasers device set on a fixed ground.

CONSTITUTION: At the same time as rubble mound at the seabled is leveled by the compactor plate 33 of a leveler 3, a horizontal laser beam 81 is irradiated onto a photo sensor 9 from a laser device 8. When the laser beam 81 is irradiated onto the centrl one of plural photoelectric converter elements aligned in the heightwise direction of the photo sensor 9, a signal corresponding to the height is outputted and compared with a reference value by a comparator. In this case, a switch valve in an oil supply pipeline to an elevating cylinder 5 is positioned at neutral place and the leveler 3 is kept at the level. On the other hand, when the level of a base ship 1 is raised under the influence of tidal wave, the elevating cylinder 5, or the leveler 5 is lowered through the switch valve because the irradiation position of the beam 81 onto said elements is lowered.