Circuit and method for A/D conversion processing and demodulation device

An A/D conversion processing circuit includes: a switch sequentially switching over multiple inputs to select each thereof according to input bandwidth of the multiple inputs or fixedly selecting a single input; an A/D converter obtaining a digital signal through sampling on a switch output with a sampling frequency according to a necessary signal bandwidth; an interpolation section performing on each signal from a separation section which separates signals included in an A/D converter output, an interpolation processing according to a sampling timing deviation in the A/D converter, to obtain a signal where the multiple inputs are digitally converted at the same sampling timing; and an output section outputting as-is an output of the A/D converter if a signal of the single input is inputted to the A/D converter from the switch, thereby allowing commonly using a single A/D converter for multiple inputs, restraining increased circuit scale and power consumption.