A charged particle beam apparatus includes a charged particle source, an aperture, an object lens, an observing unit, an aperture driving portion, and a control portion. The control portion includes a spot pattern forming portion that forms a plurality of spot patterns on a surface of a sample by irradiating a charged particle beam, an analyzing portion that calculates a position of a spot center of the spot pattern and a geometrical center position of a halo, and an adjusting position determining portion that calculates an adjusting position based on a position of intersecting lines connecting the positions of the spot centers of the respective spot patterns and the center position of the halo. In this manner, the position of the aperture can be easily and accurately adjusted in a short period of time by moving the center axis of the aperture to the adjusting position.