PURPOSE:To recognize sensually the position relation between a radio buoy and a ship at a look by displaying the position of the radio buoy on a CRT graphically together with latitude lines and longitude lines of a wake behind the ship. CONSTITUTION:An arithmetic control part 6 receives position information from various position measuring devices 13 such as a Loran navigation device and a satellite navigation device and converts the position information into CRT information together with the latitude line, longitude line, scale value, etc., calculated on the basis of the position information and a previously specified value. A graphic memory 7 is stored with the CRT information sent from the control part 6 correspondingly to CRT picture elements. A video signal generation part 8 reads the graphic memory 7 synchronously with a synchronizing signal sent from the control part 6 to generate a video signal. A reception part 11 receives a radio wave sent from the radio buoy through an antenna 10 and demodulates Loran time difference data. A receive signal processing part 12 calculates the position of the radio buoy from the Loran time difference and position data on a transmitting station.
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