To provide a method and a device for separating soil and sand from drilled muddy water, by which the soil and sand are made to meet a standard as surplus soil to unnecessitate treatment as industrial waste and the recycle of a sand part based on the sand and muddy water is realized by preventing the intermixture of a part of drilled muddy water in the soil and sand separated from the drilled muddy water, causing the sand and soil to be soft sludge.

In the basic means of the method and device for separating the soil and sand from the drilled muddy water, the soil and sand obtained as the result of drilling an underground hole 36 is lifted on the ground as the drilled muddy water with muddy water 37, the drilled muddy water is guided to a obliquely provided first vibration screen 21 to separate a pebble/clay part 40 from the drilled muddy water so accumulate it by forward sending vibration along a slope, the drilled muddy water having passed through the screen 21 is sent into a cyclone 33 and thickened muddy water discharged from a cyclone under part and including fine particles is guided to an obliquely provided second vibration screen 26 to separate a sand part in the thickened muddy water and to form the flock of the fine particles to accumulate non-fluid sand part.