There is provided a charged particle beam apparatus radiating a charged particle beam to a specimen so as to acquire an image of the specimen, the charged particle beam apparatus including: a charged particle gun that generates the charged particle beam; an electron optical system that radiates the charged particle beam emitted from the charged particle gun onto a surface of the specimen so as to scan the surface of the specimen; a detecting unit that detects secondary electrons or reflection electrons emitted from the specimen, and converts the electrons into pulse signals; a pulse signal detecting circuit that detects time detecting information regarding time of the pulse signals converted by the detecting unit, and peak value detecting information regarding each peak value of the pulse signals; and an image processing unit that generates luminance gradation of the acquired image based on a time detecting signal and a peak value detecting signal of the pulse signals detected by the pulse signal detecting circuit.