PURPOSE: To obtain the excellent circuit operation by stopping the phase comparing operation when a pulse does not arrive during the period, which is longer than the maximum period of the modulated data signal from the arrival of the pulse in a regenerated data signal, and quickly detecting the missed signal.

CONSTITUTION: Encoded read data are inputted into the input terminal of a mono-multivibrator 21 from an input terminal 20. The signal, whose constant is longer than the longest inversion period of the monostable multivibrator 21, is outputted and inputted into a NAND circuit 24. Meanwhile, a read gate circuit 25 generates the gate signal from the read data, which are supplied from the terminal 2O, and supplies the signal into the NAND circuit 24 and the read-gate-signal input terminal RG of a PLL circuit 9. In the circuit 24, the AND operation of the read-gate signal from the circuit 25 is performed, and the result is inverted. The NAND output is outputted into the circuit 9 as the control signal. When the signal is not inverted in the period longer than a period, wherein the word data are longer than the time constant, the phase comparison is stopped in the circuit 9. Thus the signal missing is quickly detected.