an id memory part memorizes an id such as a telephone number that identifies a communicant , and a use frequency memory part memorizes a corresponding use frequency . when a communication apparatus takes a sending action , a writing part receives the id from an addressee communicant and registers it in the id memory part . in case the id memory part does not have any unused memory region at this registering time , the least frequently used id is deleted from the id memory part and the memory region that becomes unused as the result registers the received id . when a communication apparatus takes a receiving action , a comparison part receives the id from an addresser communicant and sequentially compares the id with each id memorized in the id memory part , and has the communication apparatus continue the receiving action only when a conformance is detected . a use frequency updating part updates the use frequency on the use frequency memory part corresponding to the communicant &# 39 ; s id , when the communication apparatus takes a communication action . thus , an ordinary sending operation alone automatically registers the id . by properly deleting the least frequently used id on the id memory part at an automatic registering time , a new id is automatically registered without any problem , which makes the registering operation further simplified .