1. A scanning transmission charged particle beam device, comprising: a scanning coil which deflects a charged particle beam; an objective lens which focuses the charged particle beam on a specimen; a specimen stage which holds the specimen by using a mesh; an imaging device which detects the charged particle beam transmitted through the specimen; an image processing control device which processes a scanning transmission electron microscope image from the imaging device; and a monitor which displays the scanning transmission electron microscope image wherein the image processing control device displays each pixel of the scanning transmission electron microscope image on the basis of a gray value of a predetermined gradation scale; and converts the predetermined gradation scale to other gradation scale and obtains a scanning transmission electron microscope image in the case where the number of pixels of a predetermined gray value is less than a predetermined percentage.