PURPOSE: To determine the position of an own ship hyperbolic navigation system becomes impossible, by operating the intersecting points of the circumference of the circle around a ship emitting an auxiliary navigation radio wave and the hyperbola operated from the hyperbolic navigation radio waves from two transmission stations.

CONSTITUTION: Since a ship 72 is present in the areas 92a, 93a within the receiving boundaries 92, 93 of loran radio waves from a master station 82 and a sub-station 83, one hyperbola 62 can be calculated from the loran radio waves from two stations 82, 83. However, since the ship 72 is present out of the boundary 91 with respect to the loran radio wave from the sub-station 81, a hyperbola calculated by the pair with the master station 82 can not be operated and the position of an own ship can not decided and, therefore, an auxiliary navigation wave is transmitted from a ship 71. An auxiliary navigation receiving part 14 operates the distance up to the ship 71 from a time receiving the time reference mark of the auxiliary navigation radio wave 32 and transmitted time information. Next, the circumference of a circle 62 having the operated distance as a radius is operated to be outputted to a hybrid part 12. The hybrid part 12 operates the intersecting points of the hyperbola and the circumference of the circle 61 and the position of the own ship before a short time is referred to from two intersecting points to set one of two intersecting points as the position of the own ship to output the same to a display part 13.