Abstract: Apparatus for determining the positional coordinates of a moving object including a plurality of magnetic field vector detecting devices, an inclination detecting device for detecting inclination of the magnetic field vector detecting devices, a distance detecting device for detecting the distance that the moving object has travelled, and arithmetic means which receives outputs from the magnetic field vector detecting devices as well as from the inclination detecting device, calculates the horizontal component force vector of the geomagnetic field by using the outputs from the magnetic field vector detecting devices and from the inclination detecting device, further calculates the vector in the progress direction of the moving object by referring to the horizontal component force vector, and integrates the product of the vector in the progress direction and the output from the distance detecting device, whereby the positional coordinates are obtained as the output of the arithmetic means, and the coordinates