To provide an A/D conversion apparatus in which a conversion time is shortened while maintaining conversion accuracy.

A voltage/time conversion circuit 5 compares a ramp waveform voltage V1 that increases with a fixed inclination, with a reference voltage Vref1, compares an input voltage Vin1 with a reference voltage Vref2 and generates a PB pulse signal specifying times corresponding to the voltages. An encoder circuit 6 converts said times into code data TA1, TA2, TA3 corresponding to ratios in a common unit time Td, and a normalization arithmetic circuit 7 determines conversion characteristics from the code data TA1, TA3 of the reference voltages Vref1, Vref2 and A/D conversion values Lf1, Lf2 predetermined for the reference voltages Vref1, Vref2 and fits the code data TA2 for the input voltage Vin into the conversion characteristics to operate an A/D conversion value of the input voltage Vin.