The present invention relates to an analog-to-digital converting circuit, which comprises an integrating circuit, a reference signal generating circuit, a comparator, and a first counting circuit. The integrating circuit integrates an input signal for producing an integration signal. The reference signal generating circuit produces a plurality of reference signals. The comparator receives the integration signal and the plurality of reference signals, and compares the integration signal to the plurality of reference signals sequentially for producing a plurality of comparison signals. The first counting circuit receives the plurality of comparison signals produced by the comparator, and starts to count the plurality of comparison signals for producing a reset signal and resetting the integrating circuit. Because the integrating circuit is not reset once until the comparator produces the plurality of comparison signals, the number of times of resetting the integrating circuit can be reduced, and hence reducing the integral nonlinearity effect. Accordingly, the accuracy of the analog-to-digital converting circuit is enhanced.