An A/D converter including a counter for counting a clock signal to output a digital signal corresponding to an analog input signal; a D/A converter for converting the output signal of the counter into an analog signal; a comparator for comparing the analog input signal with the output signal of the D/A converter to control the counter in accordance with the comparison result; and a clock supply circuit for supplying the counter with the clock signal, wherein the frequency of the clock signal is changed in accordance with a difference signal exhibiting the difference between the analog input signal and the output signal of the D/A converter.