Scanning electron microscope

1. Field of the Invention A scanning electron microscope is provided which is capable of efficiently detecting ions, such as primary electron excitation ions, reflection electron excitation ions or secondary electron excitation ions caused by a bias electric field, thereby obtaining an absorption current. A scanning electron microscope irradiates an electron beam to a sample while keeping a sample chamber pressure at 1 Pa or higher, to detect generated ions and display a sample image. An ion detecting electrode is provided exclusively for detecting ions. The ion detecting electrode is arranged nearby a path for accelerating ions by a bias electrode.