An encoding apparatus encodes an image by tile in a smallest possible size while suppresses segmentation of a specific region in the image into tiles. Vertical lines at left and right ends of n-th face region are defined as boundary candidate vertical lines Lh(n) and Lm(n), and horizontal lines at upper and lower ends of the n-th region, as boundary candidate horizontal lines Lu(n) and Ls(n). A divider determines a horizontal line of another region existing within the range of the horizontal lines Lu(n) and Ls(n) of the n-th region as a line to be deleted. Further, the divider determines a vertical line of another region existing within the range of the vertical lines Lh(n) and Lm(n) as a line to be deleted. This processing is performed to the final region, then image data is divided using horizontal and vertical lines except the lines determined as lines to be deleted.