An A/D conversion circuit includes: first/second pulse circulation circuits delaying an input signal and circulating a pulse signal; a circulation number difference measurement section outputting a difference between circulation time numbers of the pulse signal through the first/second pulse circulation circuits; a conversion control circuit outputting the difference as A/D conversion data when outputting a conversion data output processing signal; and a signal ratio change circuit: outputting, from a first output terminal, a voltage calculated by adding the reference voltage and a voltage obtained by multiplying a differential voltage, obtained by subtracting the reference voltage from the analog input voltage, by a first proportional coefficient; and outputting, from a second output terminal, a voltage calculated by subtracting, from the reference voltage, a voltage obtained by multiplying the differential voltage by a second proportional coefficient. The first/second pulse circulation circuits receive power source voltage supply from the first/second output terminals and a ground line.