DESCRIZIONE
A sequence deciding part (10) acquires information of other ships from other-ship information signals (I), and decides the sequence of information elements of the other-ship information in descending order of probabilities of approaching the local ship. A ship selecting part (12) selects, based on the sequence of information elements decided by the sequence deciding part (10), another ship to be called up. A call-up signal generating part (14) inserts, into a call-up signal, an identification number of the other ship selected by the ship selecting part (12). The call-up signal generating part (14) then transmits the call-up signal to the other ship via a radio communication part (30) and an antenna (16).