An automatic dialing apparatus for use in a telepone or facsimile machine sends out a dial signal to an external network automatically. A detachable telephone number memory, which stores a telephone number together with an area code, is detachably mounted on a telephone unit which includes a memory storing an area code of the district in which the telephone unit is located. The area code of the telepone number data supplied from the telephone number memory is deleted if that area code agrees with the area code stored in the memory of the telephone unit. An automatic dialing apparatus is preferably constructed to carry out dialing automatically responsive to a voice. In the preferred embodiment of such a voice activated dialing apparatus, a telephone number is input through a keyboard and a corresponding identifier, typically the name of a subscriber, is voiced and its voice signal is stored in association with the telephone number.