The present invention provides an image data generating method in which a combined image is not distorted at the boundary area between a left eye image and a right eye image even when the combined image has been compressed with lossy compression among three-dimensional image data generating methods in which a combined image is generated by combining a left eye image and a right eye image. The three-dimensional image data generating method includes a combined image generating step (SA2 or SA3) in which the combined image including a buffer region between the left eye image and the right eye image is generated while the left eye image and the right eye image are arranged, and an image date compressing step (SA4) in which the picture signal of the combined image generated in the combined image generating step (SA2 or SA3) is compressed with lossy compression.