An image encoding device is provided that performs, in an image, an intra-prediction on a block obtained by dividing the image so as to encode the block, the image encoding device including: a memory; and a processor coupled to the memory and the processor configured to select a rectangular block as the block, and to add a certain prediction direction as a selection target intra-prediction direction when the rectangular block is selected, wherein the certain prediction direction is one of prediction directions in which a pixel that is adjacent to a short side of the rectangular block is referred to, and an adjacent pixel in a left or upper block that is adjacent to a long side of the rectangular block is referred to in another prediction direction that is 180 degrees opposite to the certain prediction direction.