Abstract: A modulation and demodulation system which modulates and demodulates a signal in a main channel for main data and a secondary channel for secondary data obtained by frequency division and uses, upon demodulation, a frequency timing extracted from the secondary channel as a sampling timing for an analog to digital conversion device for the main channel. The modulation and demodulation system is improved in that it can rapidly restore, when a timing error occurs, a processing condition in which a normal timing is used, and comprises a demodulation device which includes a phase timing error detection device for detecting an error of phase timing information extracted from the main channel and a storage device for storing the phase timing information. When the phase timing error detection device detects the error of the phase timing information, the demodulation device performs demodulation processing of main data using the phase timing information stored in the storage device.