1. A panoramic image generation method which generates a surrounding 360-degree panoramic image data centering around a photographing point using a plurality of photographed image data obtained by a camera, wherein, a same subject, which is an external object photographed by said camera while photographing said plurality of photographed image data, is included in each of first photographed image data which is time-serially obtained and last photographed image data which is time-serially obtained among the plurality of the photographed image data, said subject having a particular size, posture, and position in each of said first and last photographed image data dependent on a respective photographing position of said camera, the panoramic image generation method comprising: a first step of combining the plurality of the photographed image data to generate a surrounding 360-degree or more panoramic image data centering around the photographing point; a second step of performing a first process in which any of the subject of a starting end and the subject of a terminal end is deformed with respect to the subject included in each of the starting end and the terminal end of the surrounding 360-degree or more panoramic image data, to match a size and a posture of the subject of the starting end with those of the subject of the terminal end, or the first process, and a second process in which any of the subject of the starting end and the subject of the terminal end is deformed with respect to the subject included in each of the starting end and terminal end of the surrounding 360-degree or more panoramic image data, to match positions in a short length direction of the surrounding 360-degree or more panoramic image data; and a third step of overlapping the subjects respectively included in the starting end and the terminal end of the surrounding 360-degree or more panoramic image data with each other, to generate the surrounding 360-degree panoramic image data, after the second step, wherein the first process includes: a feature points extracting process of extracting feature points of the subject of the starting end and feature points of the terminal end that corresponds to the feature points of the starting end, and an image deforming process of performing a process of deforming image within any one of starting end side n-polygons each connecting adjacent n (n is a natural number of 3 or more) first feature points extracted from the subject of the starting end and terminal end side n-polygons formed by second feature points extracted from the subject of the terminal end corresponding to the first feature points, the image deforming process being performed on each corresponding pair of starting end n-polygon and terminal end n-polygon by, calculating an average deviation amount in the vertical direction between the n first feature points and the n second feature points, calculating an inclination amount based on a ratio of the average deviation amount and a lateral width of panoramic image, and deforming the image within one of the starting end n-polygon and the terminal end n-polygon based on an image deformation parameter for correcting deviation in the vertical direction, said image deformation parameter being calculated according to the following equation: ( x y ) = ( 1 0 Δ 1 ) ⁢ ( x ′ y ′ ) + ( 0 0 ) , where Δ represents the inclination amount, x′ and y′ represent coordinates of respective feature points of the one of the starting end n-polygon and the terminal end n-polygon before the image deformation, and x and y represent coordinates of the respective feature points of the one of the starting end n-polygon and the terminal end n-polygon after the image deformation.