Network telephone system and main apparatus of the network telephone system

A network telephone system for connecting a plurality of main apparatuses each accommodating at least one telephone terminal through a communication network for packet transmission, the network telephone system comprising:

• a communication unit that transmits and receives a connection confirmation signal used to confirm connection between a main apparatus accommodating a calling telephone terminal and a main apparatus accommodating a called telephone terminal when the calling telephone terminal issues a connection request between the calling telephone terminal and the called telephone terminal on the communication network, the connection confirmation signal defined by a communication protocol on the communication network;
• and
• a detection unit that detects a connection fault on the communication network on a basis of a result of the transmitting/receiving of the connection confirmation signal by the communication unit.