In this invention, the accuracy between an input analog voltage and a digital output signal can be enhanced. A background digital correction type A/D converter includes a reference A/D conversion unit, a main A/D conversion unit, and a digital corrector. The main A/D conversion unit executes an A/D converting operation at a high speed, whereas the reference A/D conversion unit executes an A/D converting operation with high resolution, respectively. Each of main digital output signals of the main A/D conversion unit and a reference digital output signal of the reference A/D conversion unit are supplied to one input terminal of the digital corrector and the other input terminal thereof respectively. The digital corrector outputs a correction-processing digital output signal. The reference A/D conversion unit includes a ΣΔ A/D converter and a Nyquist filter. The Nyquist filter suppresses a high-frequency quantization error of the ΣΔ analog-digital converter.