PURPOSE: To simplify the configuration of a circuit to separate a first pre- synchronizing pulse from a Manchester biphase signal for converting the signal to a sequence of pulse trains with a narrow duration.

CONSTITUTION: Among Manchester biphase signals TXO and TXN from a DATAC 11, the signal TXO is supplied to the trigger terminal of a D flip- flop(FF) 12 and gates 13 and 14, and a leading signal GA showing the start of a message is impressed to a reset terminal R of the FF 12. When the message is started, the FF 12 is reset, and a first pre-synchronizing pulse PPSSP is outputted respectively from the start and end of FF 15 and 16. An 'H' level is fetched into the FF 12 with the end of the synchronizing pulse PPSSP, and the following signal TXO is supplied to the reset terminal of a through counter 17. The counter 17 counts a clock TICK and outputs a pulse from a gate 18 at the starting time point of each pulse of the signal TXO and every 250nS during the continuation of the pulse.