1. A scanning electron microscope comprising: image pickup means for picking up shaded images and a secondary electron image of a circuit pattern formed on a semiconductor wafer based on a preset condition; calculation means that calculates a feature of the shaded images by calculating a normalized correlation value of the shaded images against a prestored reference image; and a computer for evaluating quality of the circuit pattern on the basis of the feature calculated by using the normalized correlation value, wherein: each of the shaded images is an image acquired on the basis of a signal detected by each of a plurality of oppositely opposed detectors provided in the image pickup means, and the calculation means independently calculates the feature of each of the shaded images obtained from the oppositely disposed detectors by calculating, for each shaded image, a first normalized correlation value from one of the oppositely disposed detectors and a second normalized correlation value from a second one of the oppositely disposed detectors.