The present invention relates to a terminal-to-terminal communication connection control method using an IP network characterized in that: in order for a mobile telephone set to have a telephone communication with a fixed telephone set by way of a mobile communication network and an IP network, the mobile communication network carries out a line connection control based on the common channel signaling system; the IP network establishing a communication path by carrying out a line connection control applying a common channel signaling system to the IP network thereby effecting a telephone communication.