PURPOSE: To make possible an operation for the correction of propagation for a prearranged period even after a differential compensation information was difficult to receive, by using a proper combination of a correction function calculated inside an omega receiving unit and correction information.

CONSTITUTION: A phase is measured 2 at input omega signal and a time elapse t-t0 from a time when updated compensation information was provided after input differential compensation information was fed to a timer 4, is measured. As to correction function generation number 5, the omega receiving unit generates a correction function f(t) calculated based on a propagation model. A calculation circuit 6 receives compensation information correction function and t-t0 and calculates a compensation volume C under a formula 1. This compensation volume C is supplied to a position calculation part 7 and phase information is sought using the phase of each omega signal from a measurement part 2. Thus phase information after propagation compensation is obtained.