In an internal line control system, a telephone having an Internet protocol (IP)
and capable of being connected to the Internet through the communication mode,
includes a device for storing an IP address of a private branch exchange, and a
device for sending a switching request to the IP address of the private branch
exchange while specifying identification information. Concurrently, a private branch
exchange having an Internet protocol (IP) and connected to the Internet through
the communication mode, includes a device for storing a correlation between the
IP address of the telephone and an internal line number depending upon the identification
information, and a device for transmitting, depending upon the correlation between
the IP address and the internal line number, a control signal and a speech communication
signal for an internal line telephone of the internal line number to an address
specified by the IP address. This allows a control to be switched over to the internal
line telephone connected to the Internet so as to inherit various types of settings
for the internal line telephone directly accommodated in the private branch exchange.