Disclosed herein is a signal level conversion circuit for increasing the dynamic range of an Analog-to-Digital Converter (ADC). A comparison and calculation unit compares the value of an input signal Vin and the value of a first reference signal Vref1 and compares the value of the input signal Vin and the value of a second reference signal Vref2, and calculates and outputs respective differences therebetween. A signal leveling circuit unit converts signal levels of the respective output signals of the comparison and calculation unit so that the output signals fall within the dynamic range of an ADC. The ADC digitizes the output signal Vo of the signal leveling circuit unit and the output signals Vack1 and Vack2 of the comparison and calculation unit.