in a digital comparator wherein a period of time taken until one output signal of a decoder circuit coincides with one corresponding output signal of a frequency divider circuit is measured by comparing output signals of the decoder circuit and output signals of the frequency divider circuit , an output circuit of the decoder circuit and an output circuit of the frequency divider circuit are constructed of integrated injection logic in order to build up wired and circuits , and further , a nor circuit which includes inverter circuits constructed of iil and a common connection line for connecting outputs of the inverter circuits in common is disposed in order to receive respective outputs of the wired and circuits . especially , the digital comparator of this invention is effective for an automatic exposure control system of a camera .