1. A scanning electron microscope comprising: image pickup means for picking up images of a circuit pattern formed on a semiconductor wafer on a preset condition; calculation means for comparing each of the images picked up by the image pickup means with a prestored reference image to thereby calculate a feature of the images picked up; and a computer for executing evaluation on quality of the circuit pattern on the basis of the feature calculated by the calculation means, wherein calculation of the feature is executed independently with reference to a secondary electron image, and each of back-scattering electron images.