PURPOSE: To make the generation of the threshold effect of a timing extraction loop hard to occur and to extract a timing signal with less jitter from a biphase signal by using an integral value for every symbol of the biphase signal to decide on the polarity of data.

CONSTITUTION: The 1st integrator 1a1 integrates data over the former half of one symbol and the integral value is held in a data delay device 6. The 2nd integrator 1a2 integrates the data over the latter half of the symbol. The integral value is multiplied by (-1) and then added to the integral value of the former half by using an adder 7, and a data detector 2 uses said addition result to decide whether the polarity of the data is 0 or 1. The 3rd integrator 1b, on the other hand, integrates the biphase signal almost at mid-pit transition and generates a positive or negative voltage in proportion to an error in zero timing when the timing relation is correct and there is the error.