A cascade A/D converter that has shorter settling time and enables high-speed operation is provided. A cascade A/D converter comprises fundamental constituent elements cascaded in plural stages, each fundamental constituent element comprising a first comparator for inputting an analog input signal, a D/A converter for converting an output of the first comparator to an analog signal again, and a subtractor for subtracting an output of the D/A converter from the analog input signal, the fundamental constituent elements comprising: a second comparator for inputting the analog input signal every least significant bit near a transition point of the first comparator; and an arithmetic operating unit for generating upper bits based on an output of the first comparator and interpolating lower bits based on an output of the second comparator.