An excavator (1) includes a frame (2) provided with suspension elements (3) for connecting to a mobile carrier, such as a tracked vehicle, as well as cutting members (8) supported on the frame (2) for digging a trench in the ground. The cutting members (8) have at least two endless series (9, 10) of cutting elements; at the same time, the cutting elements (9, 10) define a front side (11) to be turned towards a digging front and a return side (12) turned away from the digging front. Lateral guides (14) are provided on either side of the cutting members (8) for supporting the side walls of the trench.