PURPOSE: To register a telephone number which is supposed to be dialed frequently without key input operation for registering an abbreviated number by the abbreviated number registering means of the telephone set.

CONSTITUTION: A storage device 101 consists of a place 10b where telephone numbers dialed in the past are recorded and a place 101a where their frequencies of dialing are recorded, and when a telephone number dialed last time is recorded or already dialed in the past, its calling frequency is varied. When the calling frequency reaches a fixed value, the telephone number which is dialed last is displayed on a display device 106 and an operator is inquired about whether the telephone number is registered as an abbreviated number. When the operator liked to register the telephone number as the abbreviated number, he specifies the abbreviated number with numeric keys 104 and operates a function key 103 to store the telephone number in a storage device 102, thus completing the registration. When the telephone number is not registered as the abbreviated number, only the function key 103 is operated and the operation ends.