Phase difference delay control system for accommodating fluctuation in phase difference in distance measuring system

A phase difference delay control system in a distance measuring system, the phase difference control system comprising a first interface unit and a second interface unit that are connected between a reference position and a terminal via a transmission line and measuring the distance between said reference position and the terminal by transmitting a signal between said reference position and said terminal, wherein

• said first interface unit and said second interface unit comprise respective clock crossover units for sending to said transmission line the signal to which an overhead including phase information for matching the phase of a redundant signal is added, or for sending to said terminal or said reference position the signal from said transmission line from which said overhead is deleted, wherein at least a portion of said clock crossover units operates according to a reference clock signal, said respective clock crossover units including a first and a second clock crossover unit in said first interface unit, and a third and a fourth clock crossover unit in said second interface unit, and
• one of the second and third clock crossover units that operates according to said reference clock signal is notified of the fluctuation amount of a phase difference between a write clock signal and a read clock signal in one of the first and fourth clock crossover units that operates according to said reference clock signal and, upon initialization of the phase difference between the write clock signal and the read clock signal of said one of the second and third clock crossover units, a predetermined value of the phase difference is adjusted taking said amount of fluctuation into account.