A digital button telephone system which is connected to an analog public network (NW) having a function of transmitting a calling signal including the identification information of the caller through a subscriber line (CO line), incorporates a plurality of extensions to which digital button telephone sets (DKT) (2) or standard telephone sets (STT) (4) are respectively connected as extension terminals, and has a function of exchangingly connecting the subscriber's line to an extension or an extension to another extension. The system comprises terminal storing means in which the information representing the relationship between the caller and the extension terminal (2, 4) is stored in advance. When a calling signal arrives from the network (NW), the caller identification information (caller ID) included in the calling signal is detected by a caller identification information interface unit (RCIU) (12), the extension terminal to be called is determined based on the detected caller ID and the information stored in the storing means by a control unit (RCTU) (16), and the extension terminal is called through a digital telephone set interface unit (RDKU) (13) or standard telephone set interface unit (RSTU) (15).