To provide a communication apparatus that can allow an opposite communication apparatus to surely calculate a distance between the communication apparatus and the opposite communication apparatus in order to prevent illegitimate communication by other people than a concerned person with the opposite communication apparatus, and to provide a program used for the communication apparatus.

The communication apparatus is characterized in that the communication apparatus can communicate with the opposite communication apparatus that transmits a distance calculation signal for calculating the distance, receives the returned distance calculation signal to detect a phase difference between the transmitted distance calculation signal and the received distance calculation signal and calculates the distance with respect to a reply position of the distance calculation signal on the basis of the phase difference and the communication apparatus is provided with a return section for returning the distance calculation signal transmitted from the opposite communication apparatus.