To reduce an embedded depth of an earth retaining wall, by preventing settlement and drying-up of a well of the surrounding ground by excessive pumping of underground water.

In this ground excavation method, first of all, an air injection well 2 is arranged in the ground 3 so as to surround an excavation expected area 1, and the earth retaining wall 10 is built up along a boundary of the excavation expected area 1 (Step 101). Next, the boundary ground 6 sandwiched between the lower ground 4 positioned under the excavation expected area 1 and the surrounding ground 5 adjacent to the side of the lower ground, is changed to the unsaturated ground from the saturated ground by injecting air into the ground 3 via the air injection well 2, and water permeability of the boundary ground 6 is reduced (Step 102). Next, while pumping the underground water from a pumping well 9 arranged in the excavation expected area 1 in such a state, and while supporting earth pressure by the earth retaining wall 10, the excavation expected area 1 is excavated (Step 103).