To enable to detect charged particles discharged along on an optical axis.

The charged particle beam apparatus is provided with an acceleration tube electrode 30 for accelerating primary electron beams 1 from an electron gun, a magnetic field lens 2 converging the primary electron beams on a test piece 3, a speed-reduction electrode 6 for speed-reducing the primary electron beams, a scanning coil 4 for scanning on the testpiece by the primary electron beams, a detection system for detecting secondary electrons generated from the test piece 3, and a display unit 13 for displaying a secondary electron image based on the detected secondary electrons. Between the electron gun and the acceleration tube electrode 30, there are arranged a reflection electrode 34 of a doughnut shape to which a negative voltage is impressed and an Einzel lens 32 for focusing the secondary electrons from the test piece 3 on the optical axis in the tube before the reflection electrode 34 in the tube of the acceleration tube electrode 30, respectively, and the detection system is composed of a first detecting unit which has an open port through which the primary electron beams from the electron gun are passed and detects the secondary electrons from the test piece 3 and a second detecting unit which has an open port through which the primary electron beams from the electron gun are passed and detects the secondary electrons which are sent back by the reflection electrode 34 in the test piece direction.

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