To provide an excavating method in which excavation/soil improvement throughout a prescribed cross section is performed without the occurrence of unexcavated sections by excavating a plurality of noncircular cross sections.

In this excavating method for excavating the whole surface in a prescribed range by excavating a plurality of noncircular-cross-section excavated holes (H), the noncircular cross section is set to be a square cross section drawn with the locus of the vertex (M) of an equilateral triangle inscribed in a square, which is revolved with a prescribed angular speed "-3ω" while being rotated on its axis with a prescribed angular speed "ω" around the center of gravity thereof along a circumferential orbit (C) at a prescribed radius (r) from the center of the square. The excavating means is either a blade or a jet which formes at least one line segment connecting the the center (E) of gravity of the equilateral triangle with the vertex (M) thereof. The excavation is performed by revolving the excavating means in the orbit (C) with a prescribed angular speed and rotating the excavating means around the center of gravity with a prescribed angular speed. The ratio (η=L/r) of the radius (r) of the orbit (C) to a distance (L) between the center of gravity of the excavating means and the vertex thereof is selected, so that the cross-sectional shapes of the excavated holes (H1 and H2) adjacent to each other can mutually have complementarity and serve as continuous excavated cross sections.