A caller number notification synchronized with an incoming signal is disclosed. An analog circuit interface section outputs incoming call signal presence information that shows whether to receive the incoming call signal that has the information indicated at a predetermined position on a highway and outputs the received caller ID to a speech signal path. An analog extension interface section detects the incoming call signal presence information on the highway, detects the caller ID on the speech signal path, generates an incoming call signal based on the detected incoming signal presence information and sends out the generated incoming call signal and the detected caller ID to the analog extension. A system control section connects the analog circuit interface section to the analog extension interface section.