An encoding apparatus for generating, in an intra prediction mode, difference data by subtracting prediction values from input image data, and performing encoding processing on the input image data by processing the difference data. The apparatus includes a first prediction mode detecting section for detecting a first best prediction mode, a second prediction mode detecting section for detecting a second best prediction mode, and a prediction value generating section for selecting a best prediction mode. The first prediction mode detecting section detects the first best prediction mode by utilizing processing in the second prediction mode detecting section.