A device on a hydraulically powered subsea vehicle of an excavator type that is known per se, e.g., having a shovel as tool, for carrying out work on the seabed, preferably at great ocean depths, as for example depths of more than 200 metres. The vehicle has a unit for generating hydraulic driving pressure for the propulsion of the subsea vehicle and movement of the arms and links that control the tool. An automatic pressure regulating device is provided on the subsea vehicle for compensation of the pressure that the water pressure at the seabed exerts on the hydraulic system. Suction equipment may be provided for sucking away mud which is dug up by the shovel during excavation.