An oscillator control apparatus has a digitally-controlled oscillator which outputs an oscillation signal having an oscillation frequency in response to an oscillator adjusting signal, a counter which counts the oscillation signal and outputs a count in response to a reference signal in synchronism with the oscillation signal, a time-to-digital converter which calculates a phase difference between the oscillation signal and the reference signal, an adder which adds the count and the phase difference and outputs the added value as first phase information, a corrector which corrects the first phase information in response to a phase control signal for setting an oscillation frequency of the digitally-controlled oscillator when a time difference between a rising-up timing of the oscillation signal and a rising-up timing of the reference signal is less than a predetermined time, and outputs second phase information, and a filter for smoothing a difference between the phase control signal and the second phase information, to output the oscillator adjusting signal.