An image display device displays operation items of an electron microscope on an operation screen, and a storage device stores information of assist buttons which display image state information acquired via a detector of the electron microscope. The information of the assist buttons corresponds to image quality of an acquired image via the detector as well as to observation conditions composed of a combination of parameter setting values of the electron microscope, an operation program which analyzes the image quality of the acquired image. The information of the assist buttons is acquired based on analytical results of the image quality as well as current observation conditions, and the assist buttons are displayed on a predetermined part of the operation screen. Accordingly, the skills of a novice user operating a charged particle beam apparatus can be improved.