A terahertz wave generation device is provided with an ultra-short pulse laser light source (3) for generating ultra-short pulse laser light at a single repeating frequency and optical fibers (F1 to F5) for respective transmitting and projecting of the ultra-short pulse laser light to an LN crystal (15). Projection units (13) of the optical fibers (F1 to F5) are made parallel to irradiate the ultra-short pulse laser light (L) projected from the projection units (13), respectively, on terahertz transmission line (A) in the LN crystal (15) with sequential delays. The optical lengths of the transmission paths of the optical fibers (F1 to F5) are set longer as the transmission paths go closer to one side of the parallel direction of the projection units (13).