In the ocean engineering field, information about the ocean environment is important for planning, design, and operation, especially the wave information. High precision wave data is also important for considering environmental problems, like efficient operation of ships. For this purpose, many methods were considered in the past. However, an on-board directing wave measurement system has not been incorporated. The use of conventional marine radar Plane Position Indicator (PPI) images allows the estimation of wave information on a real-time basis, using both space and time information, regarding the evolution of ocean surface waves. In order to achieve data acquisition, the Radar Scan Converter (RSC) has been developed. Three-dimensional analysis was performed. The comparison of wave information derived from this system, and that of wave buoy, shows that this wave field detecting system can be a useful tool.