PURPOSE: To raise the performance and efficiency of excavation by providing a composite excavating functional device consisting of plural water jet nozzles and plural plow blades which are arranged such that the depth in excavation is orderly increased from the front stage to the back stage in the longitudinal direction in the lower part of the excavator.

CONSTITUTION: Three-stage water jet nozzles 42W44 and 42'W44' and three-stage plow blades 33W35 are provided to the lower part of the excavator 32. High- pressure water is supplied from high-pressure water generators 36 and 36' into the nozzles 42W44 and 42'W44' through flexible pressure-resistant hoses 37 and 37', pipes 38 and 38', and branched pipes 39W41 and 39'W41'. A composite cable 45 for both towing and power transmission is attached to a stabilizer for the excavator and towed on bottom under water by a working base ship (not illustrated). Electric power is supplied to the high-pressure water generators 36 and 36' through an anchor distributor 46 and lead cables 47 and 47', and water is taken into intake ports 48 and 48' to generate high-pressure water.