An electromagnetic wave emission device includes a nonlinear crystal, a prism, and a cylindrical lens. The nonlinear crystal has an optical waveguide, receives exciting light having at least two wavelength components, and outputs an electromagnetic wave having a frequency equal to or more than 0.01 [THz] and equal to or less than 100 [THz] by means of the Cherenkov phase matching. The prism includes an electromagnetic wave input surface receiving the electromagnetic wave from the optical waveguide and an electromagnetic wave transmission surface through which the electromagnetic wave which has entered from the electromagnetic wave input surface passes. The cylindrical lens has two bottom surfaces opposed to each other, a flat surface intersecting with the two bottom surfaces, and a curved surface intersecting with the two bottom surfaces and the flat surface, wherein the flat surface is in contact with the electromagnetic wave transmission surface.