A photoconductive element for performing at least one of generation and detection of terahertz radiation includes a photoconductive layer formed of a semiconductor material and configured to generate photoexcited carriers by being irradiated with excitation light, and a plurality of electrodes provided on the photoconductive layer. The material of the photoconductive layer is a material that makes a depletion layer produced in the photoconductive layer have a thickness smaller than an optical absorption length of the photoconductive layer for a wavelength of the excitation light. A film thickness of the photoconductive layer is adjusted so that the depletion layer is formed over an entirety in a direction of the film thickness within at least a portion of the photoconductive layer between the plurality of electrodes.