PURPOSE: To excavate a long and narrow trench even if the ground is relatively hard by providing a pair of cylindrical frame bodies, a guide beam constructed between the frame bodies and an excavator guided by the guide beam and reciprocated in a horizontal direction, and providing a large number of stationary excavation blades to the excavator.
CONSTITUTION: A trench excavator is constituted of a pair of cylindrical frame bodies 1 and 1, a guide beam 2 constructed between the frame bodies, an excavator 3 reciprocated with the guide beam 2 and stationary excavation blades 6 provided to the lower end edge of the excavator 3. After that, the cylindrical frame bodies 1 are inserted into longitudinal holes on a prospective trench excavation line, and the excavator 3 is horizontally reciprocated with bearing bars 10 mounted to the cylindrical frame bodies 1. At that time, earth pressure of the stationary excavation blades 6 mounted to the lower end edge of the excavator 3 is controlled to excavate. Muddy water is injected near the stationary blades 6 through a pipe line in the excavator 3, excavated earth is led to the longitudinal holes into which the cylindrical frame bodies 1 are inserted, and it is removed to the ground through air-lift type earth moving pipes l2 provided on the frame bodies 1. According to the constitution, a long and narrow trench can speedily and surely excavated even if the ground is relatively hard.