PURPOSE: To build an underground building such as a pile or an underground structure economically and in a short time by providing at the underground building such as a pile or the underground structure ground anchors placed on the slant upper side.

CONSTITUTION: A digging hole 3 is dug to predetermined depth at the ground M where a soft ground layer (n) is on the lower side of a hard ground layer (m). Next, boring holes are opened at the angle of 45 degrees through the wall surface of the hole 3 which is located at the layer (n), to the layer (m). Next, ground anchors 2 are inserted into boring holes. In continuation, anchoring bodies 2a are fixed at the layer (m) by filling up grout material into boring holes, and at the same time support bodies 4 are provided on the hole 3 side of a pile 1, and strain materials 2b are strained by means of a strain jack through support bodies 4. A reinforcing-bar made basket 5 is built into the hole 3, and at the same time fresh concrete 6 is placed, and the pile 1 of site placed concrete is built.