An organic transistor includes: a substrate made of electrically conductive material or semiconductor material; an insulating layer on the substrate; and an organic semiconductor layer and a pair of electrodes on the insulating layer, wherein a configuration is made such that: the organic semiconductor layer is sealed by a translucent member; a voltage is applied between the pair of electrodes in a range such that the organic semiconductor layer emits light; further a voltage is applied to the substrate so as to control the light emission of the organic semiconductor layer; and light emitted by the organic semiconductor layer can be taken out via the translucent member.