PURPOSE: To reduce the disconnecting frequency of a circuit and to attain the effective and economical use by performing the automatic control of a transmission data control means for improvement of the circuit using efficiency.

CONSTITUTION: A user sets a transmission original at a scanner part 12 and turns on a transmission switch through an operating part 13. An input/output control part 14 transmits the transmission original data to a compressing part 15. Then the part 15 sends the compressed data to a transmission data control part 18 which decides whether the user turned on the switch of the highest priority through the part 13 or not. If so, the part 18 sends the terminal number of the opposite party and the transmission data to a communication control part 1A. If not, the part 18 stores the transmission data in a transmission data storing part 17. When the terminal number of the opposite party and the transmission data are received from the part 18, the part 1A gives a calling request to the terminal of the opposite party and connects a circuit to send the transmission data to an ISDN circuit. A batch transmission instruction is transmitted from a timer part 19 at a set time for transmission of the stored data to the part 18. Thus the part 18 transmits en bloc the data on the terminal number of the opposite party to the part 1A.