Visual testing with underwater camera is performed for the inspection of structures in RPV. It has the case to be difficult to identify whether the indication is the crack or the imitated shape like scratch. In this case, the judgment needs much time. In this issue, the distinction method by surface ultrasonic wave emitted on the structure have been developed. This method could perform the in-situ judgment between the crack and the imitated shape by ultrasonic imaging technique with array probe.