To more stabilize a phase pulling-in operation by reducing a possibility that a frequency comparator acts as a disturbunce at the time of phase pulling-in.

The maximum value MAX of edge intervals among ≥ one frame periods and a reference value C2 are compared in an S17. In the case of MAX > C2, when the number of times of the case is ≥ a previously set value C3, the output of frequency comparisons is made an L (S26a) and the frequency of a VOC is lowered. In the case of MAX < C2, when the number of times of the case is ≤ a previously set value C4, the output of frequency comparisons is made an H (S26c) and the frequency of the VOC is lowered. In the case other than both cases, the output of a frequency comparison is made a high impedance (S26b) and the frequency comparison is disabled.