A clock generating circuit generates 2n clocks (where n is a positive integer number) each having 1/2n frequency of a maximum baud rate of data bit-stream input and a phase difference of .pi./n between successive phases thereof, and simultaneously shifts the phases on the clocks ahead or behind until the phases between the clocks and corresponding data bits of the data bit-stream input are locked in quadrature, by comparing the phase of the clock with those of data bit-stream input and adjusting the phases of the clocks.