A charged particle beam apparatus includes a charged particle beam generating system for causing a charged particle source to generate a charged particle beam. A focusing system focuses the charged particle beam onto a sample. A deflecting system causes the focused charged particle beam to scan the surface of the sample. An evacuating system evacuates a space through which the charged particle beam passes. A detector detects information obtained by irradiating the charged particle beam onto the sample. An image display system displays as an image the status of distribution of the information over the sample surface based on a detection signal forwarded from the detector. The focusing system is entirely constituted by an electrostatic lens containing a plurality of lens electrodes, one of the lens electrodes being a final electrode located closest to the sample. All of the lens electrodes except for the final electrode are supplied with positive voltages as opposed to a negative voltage to the final electrode when the charged particle beam is negatively charged (e.g., electron beam). All of the lens electrodes except for the final electrode are supplied with negative voltages as opposed to a positive voltage to the final electrode when the charged electron beam is positively charged (e.g., positive ion beam). The deflecting system is so constructed as to deflect the charged particle beam within the inner space of the plurality of lens electrodes excluding the final electrode.