Electrostatic voltmeters are generally used for potential measurements of electrostatic latent images. In this study, we are using SEM (Scanning Electron Microscope) for more detailed observation and potential measurement of electrostatic latent images; SEM can visualize electrostatic latent images as an image brightness distribution. We focused on clarification of the relation between surface potential of electrostatic latent image and brightness of SEM images. Electrostatic latent images were formed on PET (Polyethylene terephthalate) film by a corona discharger. We have observed SEM images of the electrostatic images after measuring surface potential of each latent image by using electrostatic voltmeters. We then measured distributions of brightness of the SEM images. We have successfully shown the relation between the surface potential and the brightness of SEM images. We hope SEM observation can be an alternative method for detail observations and measurements of electrostatic latent images.