PURPOSE: To simplify a circuit constitution by sending a specific pattern prior to sending a parallel data, identifying a time slot from a specific pattern received at a reception side equipment and sending an n-bit parallel data through the serial/parallel conversion at every n-bit.

CONSTITUTION: The output of a specific pattern generating circuit is selected by a selector 2 with a select signal SS prior to data transmission in a transmission equipment 101, a 1st shift register and a 1st counter apply parallel/serial conversion to the data and the result is sent to a reception side equipment 102. The reception side equipment 102 sets a set signal and detects a specific pattern from a data received by a specific pattern detection circuit 6. Then a clear signal is sent to the 2nd counter 8 to apply serial/parallel conversion and a parallel data is outputted. Then the transmission side equipment uses a select signal and a selector selects the n-bit parallel data. Moreover, the reception side equipment resets the set signal and the specific pattern detection circuit inhibits the output transmission. Thus, the transmission/reception of the n-bit parallel data is realized.