1. Electric charged particle beam microscopy wherein specimens are irradiated with charged particle beams and secondary charged particle beams generated by the specimens are detected thereby to obtain an image of the specimens, the microscopy comprising: a step of taking a first image with a known magnification to specimens by irradiating specimens with charged particle beams under a first control condition; a step of taking a second image having a common field of view with the first image by irradiating specimens with charged particle beams under a second control condition; a step of processing images for analyzing a magnification of the second image to the first image from the common field of view; a step of calculating the magnification of the second image to the specimen from the magnification of the first image to the specimens and the magnification of the second imaged to the first image; and a step of recording the magnification of the second image to the specimen along with the second control condition.