In the fishery industry, fishing nets tend to be in the water for a long time. Therefore, there is a possibility that the fishing nets will be broken by marine animals or “Kyucho”； it stands for the violent currents caused by tides or typhoons. It is necessary to repair fishing nets as soon as possible for preventing fishes from escaping to outside of the fishing net. However, a great deal of labor is required to lift and repair fishing nets. In addition, high water pressure and low water temperature may make it difficult for divers to work underwater. Therefore, underwater robot is useful to work instead of divers under such severe situations. The author suggests development of the underwater ROV (Remotely Operated Vehicle) type robot that can move on fishing net with magnet tires and repair the net using manipulators. This paper introduces the development and performance evaluation of the underwater robot using magnetic mobile mechanism.