PURPOSE: To improve the durability and the reliability of devices and economize in energy, by supplying usually power to a device which fulfills the communication function but breaking the power supply to other devices.

CONSTITUTION: Power is always supplied to a communication controller 9, a communication controller interface 14, a printer interface 8, and a printer power source controlling part 15 from the second power source 16 to secure the communication function for 24hr. Consequently, document data stored in a memory of the controller 9 is stored in a memory of the controller 9 of the other-party device under the control of a main controlling station. When receiving data stored in this memory reaches a prescribed volume, power is applied to a printer 7 from the first power source 13 through the controlling part 15 by the controller 9, and receiving data is printed out through the interface 8 by the printer 7. After printing of receiving data is terminated, the power supply to the printer 7 is broken until a prescribed volume of receiving data is stored in the memory of the controller 9 again.