PURPOSE: To realize the digital cordless telephone set having a function selecting automatically a private line or a public line in response to an area where a slave set of the digital cordless telephone set is resident.

CONSTITUTION: A slave set is provided with a memory 34 storing an ID of a master set and a memory 100 storing an ID of a nearby base station. A private/public ID changeover control section 101 of the slave set selects the private mode when the slave set detects an ID of the master set and selects the public mode when an unregistered ID is detected in the memory 100. When a registered ID is detected in the memory 100, the private ID is retrieved and when the ID of the master set is detected, the private mode is selected.