PURPOSE: To attain phase locking of a PLL circuit in a short time by providing a phase relation detecting circuit detecting the relation of phase of a data input signal and a phase variable circuit varying the phase of an output signal of a voltage controlled oscillation circuit.

CONSTITUTION: The phase relation detection circuit 26 detecting the relation of phase between output signals C', C and a data input signal (d) of a voltage controlled oscillator circuit 20 and a phase variable circuit SW1 varying the phase of the input signals C, C' to the phase comparator circuit 16 by the circuit 26 are provided. That is, the circuit 26 detects the phase difference between the data signal (d) and the clock signal to switch the switch SW1 in a way that the phase difference of both the signals is eliminated (or the phase difference is in a prescribed relation). Thus, the phase of the input signal C given to the phase comparator circuit 16 is set to a value close to the phase at the phase locking, then the phase locking is quickened.