A charged particle beam apparatus which is able to adjust charged particle optics easily in a short time with a high degree of accuracy and a method of adjusting charged particle optics are provided. A charged particle beam apparatus 1 includes a charged particle source 9, charged particle optics 12, 16 configured to set the ion beam I to a bean characteristic value corresponding to an input value to cause a sample to be irradiated therewith, scanning means 17 configured to be able to move the irradiation point of the charged particle beam I relatively with each other, observing means 32 being capable of obtaining an image, and a control unit 30, and the control unit 30 includes spot pattern forming means 33 configured to set the input value to different values and cause the sample to be irradiated with the charged particle beam I by a plurality of times at different positions to form a plurality of spot patterns and spot pattern analyzing means 34 configured to select a spot pattern having a smallest characteristic value, and sets the input values of the charged particle optics 12, 16 to a value equal to the input value corresponding to the selected spot pattern.