Provided is a terahertz wave optical device that can be used as a terahertz wave generating device including: an optical switch portion for generating a carrier abruptly by irradiation with excitation light; and a first electrode portion and a second electrode portion that are disposed so as to be opposed to each other with the optical switch portion therebetween so as to apply an electric field in a thickness direction of the optical switch portion. The first electrode portion includes, at least in part, an antenna portion having an antenna function of distributing the carrier generated by the irradiation with the excitation light in a direction crossing an application direction of the electric field. With the terahertz wave optical device, a step for adjusting the incident angle of the excitation light is simplified.