To provide a communication terminal equipment and communication system where a telephone set is available during data communication of the communication terminal equipment regardless of an inexpensive configuration.

A communication terminal equipment 5 connecting to a public line network or an extension network 4 and conducting data communication is provided with a no ringing MODEM 58 that modulates/demodulates input output data and connects to a telephone set 6 and a CPU 51 that controls the no ringing MODEM 58 and controls data communication. The CPU 51 interrupts data communication in the case that the telephone set 6 connecting to the no ringing MODEM 58 is hooked off and restarts data communication in the case that the telephone set is hooked on.