Abstract: An aiming device for guns, which comprises a transparent plate that shows to the user a critical image when the plate has a predetermined orientation, and shows a deformed image when said plate has any other different orientation. The transparent plate is so mounted in the device and the device is so mounted on the gun, such that the critical image is seen by the user when and only when the axis of the gun barrel is parallel to the line of sight passing through the user's eye and the center of the transparent plate.