A communication terminal apparatus and a communication intercepting apparatus performs a communication interception even on a communication network such as the Internet, an Intranet, or the like in which a communication route is not fixed. While the communication terminal apparatus is executing voice communication with another communication terminal apparatus, the communication intercepting apparatus transmits a monitor request signal to the communication terminal apparatus. When the monitor request signal is received, the communication terminal apparatus stores voice data which is transmitted to another communication terminal apparatus and voice data received from another communication terminal apparatus into a monitoring packet and transmits the monitoring packet to the communication intercepting apparatus. The communication intercepting apparatus receives the monitoring packet and reproduces the transmitted packets.