PURPOSE: To obtain a high-speed data transmission system of high quality which allows multiple access by allowing information data to contain an address by modulation and demodulation based upon a fixed pseudo random sequence as the address method of a transmitter and receiver in polling.

CONSTITUTION: A synchronizing signal extracting circuit 503 in a polling device in a figure extracts the clock component of a pseudo random sequence for synchronism and the frame signal of a pseudo random sequence for demodulation from a high frequency spread spectrum signal separated by a coupling circuit 500. A pseudo random sequence generator (PNGEN)504 for demodulation outputs the same sequence with the input signal of the device to a signal line 556. A discriminating circuit 507 outputs a next polling request when reading address information on it out of the data on a signal line 558. Consequently, a polling generator 508 outputs a polling signal and address information on an addressee and also drives a synchronizing signal generator 511. A PNGEN509 for modulation outputs a pseudo random signal for modulation, which is multiplied by the output signal of a POL508 and added to the synchronism pseudo random sequence signal on a signal line 565, so that the resulting signal is outputted to a power line.