Disclosed is a scanning electron microscope (SEM) for realizing high-precision dimension measurement of a sample, such as an ArF exposure photoresist, that requires the measurement of a dimension by a low S/N signal waveform. To this end, partial waveforms (or partial images) of sample signal waveforms (or an images) acquired from a dimension measurement target sample and a sample material of the same kind are registered in advance, a measurement target signal waveform (or an image) obtained from the dimension measurement target sample and the sample registration waveform are combined, and a dimension of the dimension measurement target pattern is calculated based on the combination result.