1. A panoramic image preparing method comprising a step of setting a measurement range from a known point so as to include objects to be measured, a step of dividing said measurement range as required and setting two or more sections, a step of synthesizing partial images photographed by one image pickup unit from said known point for each of said sections and preparing a panoramic image, a step of photographing each of said sections respectively under two or more contrasts and a step of synthesizing said panoramic image by using a partial image with optimal contrast out of said partial images photographed under two or more contrasts at least about said object to be measured.