1. An image generation device which generates a reconstructed image from a light field image including sub-images taken from different viewpoints, the image generation device comprising: a parameter acquiring section which acquires a photographing parameter in taking the light field image; an information acquiring section which acquires region information that decides a region of the sub-images included in the light field image based on the photographing parameter; a defining section which defines correspondence between a reconstructed pixel composing the reconstructed image and a sub-pixel in the region of the sub-images that was decided by the region information; and a generating section which decides a pixel value of the reconstructed pixel based on a pixel value of the corresponding sub-pixel to generate the reconstructed image.