This disclosure provides a navigation assisting device, which includes a TT information acquiring module for acquiring target object data by performing target tracking based on an echo received by a radar antenna, an AIS information acquiring module for acquiring target object data based on a Universal Shipborne Automatic Identification System, a maximum-number-of-output-data determination module for determining a maximum number of output data that is the number of target object data that is outputable while the radar antenna revolves once, a priority determination module for performing a priority determination according to a predetermined rule, for the target object data acquired by the TT information acquiring module and the target object data acquired by the AIS information acquiring module, and an output control module for outputting the target object data fewer than the maximum number of output data according to the priorities while the radar antenna revolves once.