An aperture adjusting device for adjusting an aperture through which light is transmitted. The aperture adjusting device includes: a chamber; a first fluid and a second fluid disposed within the chamber. The first fluid and second fluid are not mixed with each other. The first fluid transmits light and the second fluid blocks or absorbs light. A first electrode unit is disposed on an inner surface of the chamber, and includes one or more electrodes to which a voltage may be applied to form an electric field in the chamber. An aperture within the chamber through which light is transmitted is adjustable by adjusting an interfacial location between the first fluid and the second fluid by modifying the electric field.