An intra-prediction encoding/decoding apparatus and method is provided that omits transmission of prediction mode information using characteristics of reference pixels. The present disclosure provides an intra-prediction encoding apparatus and method for omitting transmission of additional information of a predicted mode of the current block through the use of characteristics of reference pixels adjacent to a current block and thereby reducing overhead when a bitstream is generated, and improving the efficiency of encoding and decoding an image while maintaining the accuracy of intra-predictions.The intra-prediction encoding apparatus includes a characteristic information calculator for calculating characteristic information of a directionality by selecting at least one reference pixels adjacent to a current block to encode, a comparer for comparing between a predetermined reference value and the characteristic information of the directionality calculated by the characteristic information calculator, a prediction mode determining unit for determining a prediction mode for the current block to be a mode corresponding to the selected reference pixel when a result of the comparison performed by the comparer satisfies a predetermined condition, and an encoder for encoding a residual between a predicted block according to the determined mode and the current block, and omitting encoding mode information of the determined mode when the result of the comparison satisfies the predetermined condition.