A communication terminal unit has a system control section including a communication error detection section that detects a communication error, which occurs at the time of originating a call over an IP network or a public network. A communication error analysis section analyzes the thus-detected communication error, and in accordance with the result of analysis of the communication error, a call origination network determination section automatically determines whether to re-dial a call over the IP network or the public network. As a result, when detecting a communication error at the time of origination of a call over the IP network or the public network, a system control section performs control operation for analyzing the communication error and automatically determining whether to re-dial a call over the IP network or over the public network.