An A/D converting apparatus includes a first A/D converter to sample an analog input signal having a D/A converter to generate a comparative signal for successive comparison with the analog input signal, a signal generator generate a differential signal between the analog input signal and the comparative signal, and a comparator to compare the comparative signal with a standard value to generate a first digital signal exhibiting high-order bit; an amplifier to amplify the differential signal to generate a residue signal; and a second A/D converter to sample the residue signal to generate a second digital signal exhibiting low-order bit.