A power factor correction apparatus is applied to an alternating-current voltage apparatus and a rear end circuit. The power factor correction apparatus includes a power factor correction unit, a control unit, and a ripple detecting unit. The power factor correction unit is electrically connected to the rear end circuit and the alternating-current voltage apparatus. The control unit is electrically connected to the power factor correction unit. The ripple detecting unit is electrically connected to the rear end circuit, the power factor correction unit, and the control unit. The control unit is informed by the ripple detecting unit to control the power factor correction unit to adjust the power factor after the ripple of the signal outputted from the power factor correction unit is detected by the ripple detecting unit.