According to the present invention, an electromagnetic wave emission device includes a nonlinear crystal having an optical waveguide; and a prism including an electromagnetic wave input surface and an electromagnetic wave transmission surface. The electromagnetic wave transmission surface includes a rotation surface which is a trajectory of a tilted line segment rotated about a central axis of the electromagnetic wave input surface, the tilted line segment being tilted with respect to the central axis. The tilted line segment and the central axis are on the same plane. The central axis is in parallel to an extending direction of the optical waveguide. The central axis passes through a projection of the optical waveguide into the electromagnetic wave input surface.