1. A stereoscopic image display apparatus for generating and displaying a stereoscopic image that forms a three-dimensional image comprising: a viewer's point setting unit that sets a point of view of a viewer seeing an object of a size greater than a critical parallax boundary; a critical parallax calculating unit that calculates a critical parallax that is the boundary of a parallax capable of forming a three-dimensional image which is in focus on a retina of the viewer from the point of view of the viewer; a rectangular parallelepiped dimension calculating unit that calculates the dimensions of a rectangular parallelepiped inscribing a sphere having a diameter equal to the calculated critical parallax; an estimating unit that estimates a space using the calculated rectangular parallelepiped and including the object; a space dividing unit divides the estimated space into multiple spaces based on the calculated rectangular parallelepiped and disposes those spaces until the object is not included therein; a focus point setting unit that sets focus points for the multiple spaces, respectively; a focus image generating unit that generates a stereoscopic image for the each of the multiple spaces, with respect to the point of view of the viewer and the focus point; a focus image pasting unit that pastes the generated multiple stereoscopic images together to generate a single stereoscopic image, said focus point image pasting unit comprises: a unit for calculating the brightness difference by using one space of the divided spaces as a reference, calculating the difference between the brightness value of a stereoscopic image generated in said one space and the brightness value of a stereoscopic image generated in another space adjacent thereto, a unit for moving the other space in parallel with said one space and for recalculating the brightness difference; and a unit for obtaining the relative position of the other space with respect to said one space, at which the calculated brightness difference becomes minimal; and an image displaying unit that displays the generated single stereoscopic image.