An A/D converter includes an A/D conversion circuit for converting an analog output signal into a digital signal, and a control circuit for controlling the A/D conversion circuit. The control circuit acquires a digital signal of a first bit indicating which level regions the voltage level of the analog output signal corresponds to in accordance with a first conversion operation by the A/D conversion circuit, sets a reference voltage corresponding to the level region based on the first bit, amplifies the difference voltage between the analog output signal and the reference voltage to correspond to the A/D conversion input range of the A/D conversion circuit, outputs an amplified analog signal, acquires a digital signal of a second bit indicating the voltage level of the amplified analog signal in accordance with a second conversion operation by the A/D conversion circuit, and synthesizes the first bit and the second bit.