An infrared sensor includes an infrared generator for generating infrared radiation within a detecting area, a pyroelectric sensor, a microprocessor, and an integrated detecting processor. The pyroelectric sensor is electrically communicated with the infrared generator, wherein the infrared radiation as an input signal is converted into a DC signal as an output signal having a real signal with low frequency and a noise signal mixed therewith. The microprocessor includes an A/D converter electrically connected with the pyroelectric sensor, wherein the microprocessor is arranged to receive the DC signal for data processing. The integrated detecting processor, which is electrically connected with the microprocessor, is adapted for stripping out the DC signal from the pyroelectric sensor to control a DC level of the DC signal, such that the real signal is allowed to be accurately processed in the microprocessor without data overflowing.