In an image forming method of charged particle beam apparatus for scanning a sample by irradiating the sample with a converged charged particle beam and detecting secondary charged particles generated from the sample by a detection unit, receiving and processing an output signal from the detection unit, and receiving the processed signal and forming an image of the sample, receiving and processing the output signal are performed by analogically processing the output signal and by performing pulse-count processing on the output signal, and pulse-count processing is performed by removing a ringing pulse in the output signal and counting pulses in the signal from which the ringing pulse has been removed.