There is disclosed a phase-locked loop (PLL) circuit for use in an improved deflection correction circuit for a larger and flat display device. The PLL circuit has a phase comparator circuit, a filter, and a voltage-controlled oscillator (VCO) connected in series in this order. The output signal from the VCO is fed back to the phase comparator circuit. The PLL circuit further includes a period-detecting circuit for detecting the period of an externally applied signal and a frequency divider circuit. This frequency divider circuit divides the frequency of the output signal from the VCO according to the period detected by the period-detecting circuit and feeds the resulting signal back to the VCO.