Abstract: A sample CD measurement system adapted for measuring the CD of a measurement portion accurately even in the case where the shape of the measurement portion and the direction of measurement are arbitrary. Before the CD measurement, a measurement reference image corresponding to the measurement portion is registered in a computer and controller. At the time of the CD measurement, the measurement reference image is read and compared with an image of the measurement portion to thereby obtain a difference in shape between the image of the measurement portion and the measurement reference image on the basis of a result of the comparison to thereby obtain the CD of the measurement portion on the basis of the difference in shape.