To surely prevent a terahertz light generating element from causing dielectric breakdown and to enhance an intensity of the generated terahertz light.

The terahertz light generating element 1 comprises a substrate 5 as an optical transmission unit, and conductive films 6, 7 as two conductive units formed on one surface of the substrate 5 and separated from each other. The films 6, 7 are disposed at a predetermined interval (g) in a direction along an upper side flat surface of the substrate 5. Excited pulsed light is emitted from an emitting unit 2 to a predetermined position of the element 1. A bias voltage is applied between the films 6 and 7 from a DC power source 3. Wires 4a, 4b as two conductors for constituting a discharge unit 4 are respectively electrically connected to the films 6, and 7. When an overvoltage is applied, a discharge occurs between distal ends of the wires 4a and 4b so that the element 1 is protected against a dielectric breakdown.