A filtering apparatus calculates a median of image data that includes nine pixel values arranged in a window of 3*3. First, an input circuit receives as an input the image data, divides the data into groups each having three pixels, and outputs. The pixel values of each group are sorted in accordance with magnitude order, by a plurality of sorters. After sorting, the maximum values among the pixel values of the groups are determined by a plurality of shifters and a plurality of maximum value determiners, and the determined pixel values are removed from the corresponding groups. As a result, four largest pixel values are removed from the three groups. A last sorter extracts and outputs the maximum pixel value (median) from the remaining five pixel values.