In a telephone system, which is arranged by a parent telephone unit and a plurality of child telephone units capable of radio-communicating with the parent telephone unit, the parent telephone unit includes a telephone number data storage table for storing a plurality of telephone number data indicative of a plurality of telephone numbers commonly usable by the plurality of child telephone units. The parent telephone unit retrieves the telephone number data storage table in response to a telephone number retrieve command issued from each of the plural child telephone units, and outputs a retrieve result to such a child telephone unit which has issued the telephone number retrieve command. Each of the plural child telephone units issues the telephone number retrieve command as a retrieve command issuing child telephone unit. Each of the plural child telephone units enters the retrieve result outputted from the parent telephone unit, and also outputs the entered retrieve result to a user of the retrieve command issuing child telephone unit.