1. A computer-implemented method for producing a multi-viewpoint image for three-dimensional image display which acquires a multi-viewpoint image used for three-dimensional image display for providing parallax in a horizontal direction to cause a viewer to recognize a three-dimensional image, comprising the steps performed by a processing unit of a computer of: setting, by the processing unit, a plurality of viewpoints to be spaced at equal intervals in direction perpendicular to a single reference projection plane including target viewpoints serving as references that are spaced at constant intervals in a first direction parallel to the reference projection plane; setting, by the processing unit, a plurality of individual target viewpoints which are respectively different from the target viewpoints serving as the references and serve as feet of a perpendicular to the plurality of viewpoints, corresponding to the respective viewpoint, on a projection plane which is a plane including the reference projection plane; while the shapes and the areas of the individual projection planes which are regions in the projection planes of images acquired from the plurality of viewpoints are kept constant, making a determination, by the processing unit, such that the shapes and the sizes of the individual projection planes are included in the reference projection plane in overlapping regions of the individual projection planes acquired from two viewpoints positioned at the outermost positions of the plurality of viewpoints; and cutting out, by the processing unit, regions of the reference projection plane from the individual projection planes acquired from the respective viewpoints to form a multi-viewpoint image for three-dimensional image display, wherein the cut-out regions are shifted in position in horizontal and vertical directions for the respective viewpoints.