A digital phase detector includes a quantization unit that quantizes a frequency of a reference signal to generate reference delay information and reference integer phase information, and quantizes a frequency of an oscillation signal to generate oscillation delay information and oscillation integer phase information. A first conversion unit converts the frequency of the reference signal into reference frequency information based upon the reference delay information and the reference integer phase information. A second conversion unit converts the frequency of the oscillation signal into oscillation frequency information based upon the oscillation delay information and the oscillation integer phase information. A calculation unit converts the reference frequency information and the oscillation frequency information into first and second phase information, respectively, and outputs a digital phase difference between the first phase information and the second phase information.