Abstract: An undercut trenching machine for digging a ground trench and removing the spoil therefrom wherein the trench is advanced first at the bottom. A cutter chain is carried on a cutter bar that is mounted at its upper end for pivotal movement on a drive unit. A tractor unit is operatively connected to the drive unit by an extensible and retractable boom. In operation, the cutter bar is inclined downwardly and forwardly of the drive unit so that earth is cut or loosened along the upwardly and forwardly facing edge of the cutter. Spoil is conveyed atop the cutter chain to the drive unit which diverts it to either side of the trench.