1. An apparatus for evaluating optical characteristics of an optical system based on an image forming position of a point image that is formed from a point light source through the optical system, the apparatus comprising: a point image producing unit that has a plurality of the point light sources positioned in vicinity of an object surface of the optical system and arranged in a planar form, and forms a plurality of the point images through the optical system from the point light sources; an imaging unit that images a plurality of the point images to produce a point image distribution image; a moving unit that changes relative distance between the optical system and the point light source or the imaging unit in an optical axis direction of the optical system; an imaging control unit that controls the moving unit to change the relative distance, and controls the imaging unit to image the point image distribution image in every change of the relative distance; an image axis shape calculation unit that performs processing of detecting an image forming position in each different relative distance of the point image based on image information of a plurality of the point image distribution images imaged at the different relative distance, the processing including calculating a regression expression concerning the image forming position and the relative distance for each of the point images to obtain a shape parameter of the image axis determined by the regression expression in each of the plurality of point images; and an evaluation value calculation unit that fits a characteristic distribution model function representing distribution of the optical characteristics to the shape parameter in each of the plurality of point images, and calculates an evaluation value of the optical characteristics based on the fitting characteristics distribution model function.