Monitoring connection state between main equipment and terminal in network telephone system

A main equipment is used in a network telephone system including telephone terminals and the main equipment. The telephone terminals are connected to a communication network to transmit voice packets. The main equipment connects the telephone terminals to one another through the communication network to cause the telephone terminals to communicate with each other. The main equipment includes a communication unit and a detection unit. The communication unit transmits connection confirmation signals to the telephone terminals at different timings, respectively. The connection confirmation signals are defined by a communication protocol on the communication network. The connection confirmation signals are used to confirm connection between the telephone terminals and the main equipment. The detection unit detects presence of one telephone terminal when the one telephone terminal sends back a response signal in response to the transmission of the connection confirmation signals.