To provide a sample image length measurement method by which the measurement area can be set by easily, quickly and surely performing matching of a plurality of standard images and the sample image even when the obtained sample images are various on the basis of a pattern forming condition of a pattern forming device such as a stepper.

In this sample image length measurement method by applying the electron beam onto a sample, forming the sample image by charged particles generated from the sample, and measuring the length of a pattern of the obtained sample image, a plurality of standard images 36, 37 are prepared by extracting the characteristic shape of the pattern 35, the pattern matching to the sample image is performed on the basis of the prepared plurality of standard images 36, 37 to set the measurement area to the pattern 35, and performing the length measurement of the sample image in the set measurement area 38.

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