PURPOSE: To add the residence time of a mobile station by detecting the position of the mobile station and resetting a residence time detecting circuit when either the position detected values of the horizontal and vertical axes or the residence time of the mobile station exceeds prescribed time.

CONSTITUTION: When a position detector 1 detects the position of the mobile station in a unit interval, the detector 1 decomposes the detected position into the unit distances of X and Y axes and stores the unit distances in memories 11 and 12. Further, the X and Y axes of the position of the mobile station in the unit interval when a residence time detecting circuit 19 is reset are respectively stored in horizontal and vertical axis memories 14 and 15. Horizontal and vertical axis unit distance difference detecting circuits 16 and 17 respectively compare stored contents Δx and Δy of the horizontal and vertical current position memories 11 and 12 and contents X and Y of the memories 14 and 15 and detect deviations Δx-Y and Δy-Y. When differences equivalent to prescribed distances or above are respectively obtained for these deviation values, a reset circuit 18 resets the circuit 19 and sets the stored contents of the memories 14 and 15 to the horizontal and vertical axes of the new current position of the mobile station after the mobile station moves, namely, the memory values of the memories 11 and 12.