A versatile apparatus for demonstrating the imaging properties of various types of electrostatic lenses, designed and constructed in this department, is described. The chief merits of the apparatus are the simplicity and the facilities provided for externally maneuvering the lens elements in several respects without disturbing the vacuum. The apparatus is used regularly by students in their laboratory experiments to study the focusing properties of different types of electrostatic electron or ion lenses or their combinations, as a part of the laboratory course on electron and ion optics.