PURPOSE: To attain efficiently a simple n:n data communication by discriminating whether or not collision takes place depending whether or not an identification number in a carrier signal transmitted from the own station is received normally by the own station.

CONSTITUTION: A code transmission section 62 outputs a carrier code 31 or a data code 41 to a line 14 in the timing generated from a supervisory timer section 63, as a data signal 40 comprising consecutive codes 41 for the code 41, and carrier signal 30 for the code 31 in the time interval of the time width of carrier code. A generating section 65 reads an identification number of the own station from a set section 69 and transfers it to a transmission section 62 as the code 31. A data check section 71 checks whether or not the constitution of the signal 40 is coincident with the data form and checks by using a check code 55. When the check shows no fault and the identification number of an identification number code 53 is coincident with the own identification number set to the set section 69, it is discriminated as the signal 40 for the own station and a received data 72b of the data section 54 is transferred to a data processing section 72.