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Water current and echo intensity data obtained with an Acoustic Doppler Current Profiler (ADCP) which is attached to a cabled observatory on deep seafloor were evaluated in situ by comparing current velocity data with those obtained with moored current meters which were temporarily deployed and by investigating artificial disturbance that appeared on both current velocity and echo intensity which were caused by a Remotely Operated Vehicle (ROV) and a manned submersible. As the result, current velocity data obtained with ADCP were roughly correlated well in long period with those with moored current meters, although there were discrepancies in short period to some extent which would probably be associated with seafloor topography at the observation site. As for the artificial disturbance caused by an ROV and a manned submersible, the acoustic noise caused by them did not seem to affect current velocity data nor echo intensity of ADCP except when they worked very close to the observatory. On the other hand, water current fluctuation caused by the ROV was observed especially when it was descending and ascending. The increase of echo intensity at corresponding altitude which was caused by the reflected acoustic signal from the submersible was clearly observed when it came across the area within the angle of about fifteen degrees from the axis of a transducer of ADCP. Additional utilization of ADCP such as detection of marine mammals larger than a submersible "Sinkai 2000" like diving whales could be possible that would be important for marine ecological study.