Abstract A new method that makes possible a potential profile measurement of an electrostatic latent image is proposed. When the surface potential is greater than the acceleration voltage of the primary electron, the velocity becomes zero before the electron hits the sample. As a result, the primary electron reaches a detector without reaching the sample. The surface potential profile can be measured by detecting primary electrons while changing the applied voltage to the substrate of a photoconductor. The significant feature of this method is that the charging, exposure, and detection devices are all incorporated in the same system, making real-time measurement possible. In order to confirm the phenomenon of reciprocity law failure, the potential depth of the latent image was measured by changing the delay time when double-pulse exposure was carried out. As a result, the latent image potential tends to be formed deeper as the delay time becomes longer. The developed Electrostatic Latent Image Measuring System (ELIMS) has good performance with a measurement potential resolution of 2 V.