PURPOSE: To enable transmission, by detecting errors of PCM data at an error detection circuit, replacing the data into those of positive or negative peak value in detecting errors, and adding the result of error detection with the data without providing special memories.

CONSTITUTION: PCM data are fed to an error detection circuit 20 with the error detection code to detect the error in PCM data. Further, if there is no error, the output of the circuit 20 makes the switch 30 as the terminal N, and the PCM data delayed by one frame at the delay circuit 80 is written in the memory 10. Further, if any error is detected, the switch 30 is switched to the terminal E and the data of positive or negative peak value is produced from the peak value data generating circuit 40, and the data with this peak value is written in the memory 10 via the switch 30. The output from this memory 10 is converted into parallel data at the serial/parallel conversion circuit 50, the error in the input data is detected with the peak value at the error data detection circuit 70 and error correction is made at an error correction circuit 60.