A power factor correction device includes a rectifier for converting an AC input voltage into a DC input voltage, an output module for generating and outputting a DC output voltage, an intermediate inductor coupled between the rectifier and the output module, a power switch for controlling an inductor current of the intermediate inductor and generating a source voltage, a reset module for generating a reset instruction according to the DC input voltage, the DC output voltage and the source voltage, an SR flip-flop for outputting a latch result according to a set instruction and the reset instruction, and a set module for generating the set instruction in response to variation of the intermediate inductor or variation of the latch result.