A double-integrating A/D converter in which an integrator output voltage, produced by integrating an analog signal input thereto, is reverse-integrated in accordance with a reference voltage having a polarity opposite to that of the analog signal. The time required for the reverse integration is measured in the form of a pulse count by means of a counter. A microcomputer for controlling the counter and a switch which selects the input to the integrator are provided with a software timer function so that the integrating interval of the analog input signal is set at will. The microcomputer also is capable of calculating a digital value, which corresponds to the analog signal, from a count recorded in the counter and from an overflow value indicated by an overflow signal generated by the counter. The signal converted by the A/D converter is capable of being applied to the weighing section of an electronic weigher.