1. An image processing apparatus comprising: an image synthesis unit generating a synthesized image by inputting a plurality of images photographed at different positions and connecting strip areas cut from the images, wherein the image synthesis unit generates a left-eye synthesized image applied to display a 3-dimensional image by a process of connecting and synthesizing left-eye image strips set in the images and generates a right-eye synthesized image applied to display a 3-dimensional image by a process of connecting and synthesizing right-eye image strips set in the images, and wherein the image synthesis unit performs a process of setting the left-eye image strip and the right-eye image strip in an allowable range of set positions of the left-eye image strip and the right-eye image strip used to generate the left-eye synthesized image and the right-eye synthesized image, which are at different observing points, applicable to display the 3-dimensional images by acquiring the allowable range from a memory or calculating the allowable range.