1. An encoding apparatus using intra prediction, the encoding apparatus comprising: a reference pixel characteristics extractor for receiving one or more reference pixel included in neighboring blocks of a target block to be encoded to determine a reference pixel characteristic and determining whether an adaptive filtering is applied to the one or more reference pixel, based on the reference pixel characteristic; a first intra predictor responsive to when the adaptive filtering is determined by the reference pixel characteristics extractor to be applied for comparing between results of performing an intra prediction using a high-frequency filtered reference pixel and an intra prediction using a high-frequency-unfiltered reference pixel to output cost-efficient one of the results involving costs along with filtering information indicating whether to perform filtering or not; and a second intra predictor for outputting the result of performing the intra prediction using the high-frequency-unfiltered reference pixel when the reference pixel characteristics extractor determines that the adaptive filtering is not to be applied.