PURPOSE: To prevent the abnormal shift of an omega position, by calculating a lane number by calculating the initial estimation position at the last time of office selection from the difference between the initial estimation position, when the previous office selection was altered, and an actual omega position and the elapse time from the time when the previous office selection was altered.

CONSTITUTION: From the elapse time of a timer part 5 from the time when the previous office selection was altered and the difference between the initial estimation position of a memory part 4 at the time when the previous office selection was altered and the omega position after an initial lane was set, an omega final position before the last office selection is calculated by an LOP calculation part 3 to be outputted to an output terminal 7. The output signal is subjected to coordinates conversion to be inputted to an estimation position input terminal 6 and read by the LOP calculation part 3. An initial estimation position of this time is determined by the calculation part 3 to calculate an initial lane number.