PURPOSE: To save useless fall back control by deciding a system and a constant used for a facsimile communication on the basis of a value with experienced results and adopting a communication by a speed suitable for the line characteristic for communication.

CONSTITUTION: An input from a ground input mechanism 21 is converted into a ground code at a ground recognizing circuit 12 and inputted to a constant memory circuit 10. On the other hand, values of the system and constant corresponding to the ground code are outputted from a constant input mechanism 20 and they are inputted to a constant decision circuit 13 via an accumulated data memory 31 as an initial value. An output of the constant memory circuit 10 accessed by the ground code is fed to the constant decision circuit 13, where the system and constant used for the facsimile communication are decided. A system control section 26 starts communication based on the result. On the other hand, the constant is changed depending on the communicating conditions in the process of communication. For example, if the quality of line is bad, the communication speed is reduced and the value decided finally is fed back from the system control section 26 to the accumulated data memory 31 and stored.