A contactless conductance potentiometer is provided in which the total conductance between two electric terminals can be selectively divided, the two parts being equal to the total conductance. This can be accomplished by using a ring-shaped photoconductor on a substrate, the ring-shaped photoconductor being divided along a diametral line. One exterior electrode is located on the substrate in a position surrounding one portion of the ring-shaped photoconductor and being in contact with the marginal edge thereof. The remaining part of the ring-shaped photoconductor is in marginal contact with the second exterior electrode. A tapping electrode is mounted inside the ring-shaped photoconductor and is in marginal contact with the inner edge of the ring-shaped photoconductor. The construction is such that when the photoconductor is exposed to light falling on the combined ring-shaped parts, current will flow through the exposed part of the photoconductor between the tapping electrode and one of the two exterior electrodes.