PURPOSE: To provide the communication equipment able to make communication without a problem by allowing a called party after reaching a communication state to automatically recognize the operating system of a caller side and allowing the called party to match its own system to the recognized system without knowing the operating system in advance between two transmission reception devices.

CONSTITUTION: In the communication equipment in which all bit data are used for data communication and half of bits are used for talking and the half bits are used for data communication and the two systems are used selectively, the equipment is provided with circuits 21,22 detecting a flag pattern '01111110' in each signal line in the operation of each system, and the operating system is discriminated automatically depending whether the flag is detected in any system of the bit pattern signal at the start of communication and the called side equipment is switched into the system detected as above. Thus, the called party side recognizes the operating mode of the caller side automatically and makes communication in matching with the recognized mode, then efficient communication is implemented.