According to the present invention makes, even if two of mobile communication terminal apparatuses such as a wireless key apparatus and a mobile telephone terminal apparatus or the like are utilized in various possessing states, it is made possible to maintain a stable distance detection accuracy. In a communication apparatus in which A distance to a connection partner terminal is detected according to a certain parameter and in a case when the distance exceeds a predetermined value, a function limitation or notification to a user is carried out, it is identified that the two of the mobile communication terminals lie in a predetermined appropriate distance according to a manual or automatic method and the proper distance identification information and further receiving state and transmission power at that time if they are necessary are communicated mutually and a parameter used for a distance detection is adjusted.