Disclosed is a power factor correction circuit for varying an output voltage according to an input voltage, and an output voltage control method thereof. A reference voltage is generated corresponding to a voltage at an output terminal of a boost circuit at a predetermined time by using the status in which the voltage at the output terminal thereof has information on an input AC voltage until the predetermined time after the input AC voltage is applied in the boost circuit. The output voltage is controlled to be generated according to the reference voltage. Therefore, the output voltage is generated corresponding to the input AC voltage without any additional devices, and reduces power loss.