PURPOSE: To construct a ditch for an installed body easily by performing a series of work, that is, ditch excavating, ground solidifying material spreading, excavating-mixing-agitating and smoothing work at the same construction site.

CONSTITUTION: A ditch of specified width and depth is continuously excavated in the ground 10, and ground solidifying material 14 is spread to the specified thickness at a bottom part 13. While excavating the bottom part 13 to the specified depth, the ground solidifying material 14 and excavated sediment are mixed and agitated to make the bottom part 13 uniform soil 15 to the specified depth. The uniform soil 15 is smoothed into the flat installation face 16 and then cured so as to be made into an installation ditch 17 of hard ground with the flat installation face. A pipe 18 is installed thereon, and filling 12 is back-filled to bury the pipe 18 in the ground. Uniforming work is performed before the excavated-mixed-agitated part is sufficiently hardened. The ditch for installing the pipe can be constructed easily in a short time by ditch excavating work, ground solidifying material spreading work, excavating-mixing- agitating work and smoothing work.