The present invention can suppress the decline in video quality during encoding. The present invention generates, for each of the nine intra image prediction modes preset according to the AVC standard, a difference image data item containing a difference value from pixels surrounding a process-target pixel. Then, an encoding device (10) ranks the intra image prediction modes depending on the sum of absolute difference (SAD), which is the sum of differences that is based on the sum of absolute values of each process-target pixel of the difference image data item and a preference order of offset[n] preset for the intra image prediction mode.