The present invention comprising: a first local oscillator for generating a first frequency; a second local oscillator for generating a second frequency; phase-difference setting means for setting a first phase difference between a transmission signal and an output of the aforementioned first local oscillator; phase-difference detection means for detecting a second phase difference which is the phase difference between a reception signal and an output of the aforementioned second local oscillator, and calculation means for calculating a distance to a communication counterpart from a third phase difference and a fourth phase difference which are notified by the communication counterpart, and from the aforementioned first phase difference and second phase difference, wherein the third phase difference is set to the second frequency by the communication counterpart, and the fourth phase difference is set to the first frequency by the communication counterpart.