1. An electron microscope having: an irradiation lens system configured to irradiate an electron beam to an observation target; an objective lens system configured to focus on the observation target; a detection device configured to detect a response from the observation target; an image forming lens system configured to adjust a size of the observation target to a specified size when the observation target is projected on the detection device; a selection mechanism configured to select an area of the observation target projected on the image forming device; an operation device configured to perform various types of operations; and a display device configured to display an image produced by the operation device or an image detected by the detection device, the electron microscope comprising: a first detection means configured to detect, by the detection device, an image in which an observation range of the observation target is not selected by the selection mechanism; a storage means configured to store an image detected by the first detection means; a second detection means configured to detect, by the detection device, an image in which an observation range of the observation target is selected by the selection mechanism; an extraction means configured to extract an outline of the selection mechanism from the image detected by the second detection means; a drawing means configured to draw the outline, which is extracted by the extraction means, on an image shot by the first detection means; and a display means configured to display the image drawn by the drawing means.