A PFC boost converter is a non-linear system whose small perturbation model is changed at each operating point depending on a duty ratio. The robust controller for the PFC boost converter is needed to suppress the output voltage change at load sudden change while attaining high power factor and low harmonic. In this paper, the combining method and design methods of twoapproximate 2-degree-of-freedom (A2DOF) controllers which simplify the overall controller and attain good robustness are proposed. The proposed controller is actually implemented on a Micro-processor and is connected to the PFC boost converter. Experimental studies demonstrate that the proposed robust controller is effective to suppress the output voltage change to improve power factor and to decrease harmonic.