PURPOSE: To improve levelling efficiency, by a method wherein an impact force is exerted on a bottom plate through the drop of a hammer within a casing formed integrally with the bottom plate, and levelling is effected through transmission of a striking force to a sea bottom ground through the medium of the bottom plate.

CONSTITUTION: A levelling device 1 is formed such that the lower end of a casing 2 is formed integrally with a bottom plate 3, and the casing 2 is formed so as to have size enough to allow incorporating of a hammer 4. The levelling device 1 is lowered onto the sea bottom as it is suspended by means of a crane, and the hammer 4 is freely dropped within the casing 2. Since horizontality of the bottom plate 3 is ensured, an impact force produced by the drop of the hammer is vertically exerted. This enables maintenance of vertical direction properties of an impact force generated by the hammer, and practically prevents energy loss produced until the hammer drops down to a bottom ground, resulting in the possibility to perform more efficient levelling.