A photoconductive device includes: a photoconductive layer configured to generate carriers upon irradiation with excitation light, a first electrode arranged on the photoconductive layer, a second electrode arranged on the photoconductive layer with a gap between the first and second electrodes, and a third electrode arranged in a region over which an electric field caused by voltages applied to the first and second electrodes or an electric field caused by irradiation with a terahertz wave extends. A depletion layer of the photoconductive layer is controllable by a voltage applied to the third electrode.