The influence of the working distance and accelerating voltage on the backscattered electron signal in an SEM, from which surface topology can be processed, was investigated. An SEM equipped with four detectors was used. The signal for a small, 0.5 mm steel ball, taken as a reference, was observed. The signal intensity was qualitatively represented by the pattern of stripes due to the level of the intensity on the sphere surface. The level was observed along the circle passing through the pole of the ball and crossing the stripes. Looking at the normalized signal, which is a signal divided by the sum of those from four detectors, we found the most preferable property at a distance 14mm from the sensitivity and the sufficient intensity of the signal view point. The normalized signal for the accelerating voltage could be adjusted to a single characteristic. This means that it could be chosen by taking the sensitivity and the effect of the beam to the materials into account.