Leveling work of rubble mound is one of the typical work of port construction. At present, this work is mainly carried out by hand by divers. However, it is hard-duty work for divers. Therefore, there are cases where machines are used for the work. One of them is underwater backhoe. In this method, a diver operates the underwater backhoe in the water. There is room to reduce the burden on the diver. To reduce the work load, we studied the possibility of remotely operating the leveling work and identified the problems to be solved. One of the problems is the decrease in work efficiency.
　In this study, we propose a new attachment to improve the efficiency of remote control with simple operation. The proposed attachment is based on a commercially available hydraulic hammer. The attachment is installed a pressure plate on the tip of the hammer.
　The test device was developed and performance tests were carried out on a full-scale mound model made of rubble on land. The test showed that the machine was capable of leveling the mound surface with a maximum height difference of 400 mm to within that of 200 mm. However, it was confirmed that the system was not capable of leveling areas lower than the target height.
　After that, an underwater test in an actual construction field was conducted using an underwater backhoe operated by a diver. As a result, the ability to settle and level the mound in water was confirmed. The performance to push down the mound was about 11 cm in 5 seconds and about 25 cm in 30 seconds. In addition, when the machine guidance system developed by the authors was used in combination, the unevenness mound with a maximum of 150 mm could be leveled within the target unevenness.
　In order to solve the problems in the land-based test, a small bucket for moving stones was attached to the test equipment, and a test was conducted on land. As a result, it was confirmed that the proposed attachment can level a mound with a maximum height difference of 600 mm to a target unevenness which has height difference of 400 mm. These results indicate that the proposed attachment is useful for leveling work.

Key Words: port construction, underwater excavator, leveling attachment, sea experiment