An electromagnetic wave emission device comprising: a nonlinear crystal that receives excitation light (Lp) having at least two wave length components and outputs an electromagnetic wave having a frequency between 0.01 [THz] and 100 [THz] through the Cherenkov phase matching, the nonlinear crystal having an optical waveguide; a prism that includes an electromagnetic wave input surface which extends parallel to the optical waveguide and which receives the electromagnetic wave from the optical waveguide and an electromagnetic wave transmission surface through which the electromagnetic wave that has entered the electromagnetic wave input surface transmits; and a buffer layer arranged between the prism and the nonlinear crystal, wherein: the prism is attached to the buffer layer; the electromagnetic wave transmission surface includes a rotation surface which is a trajectory of a tilted line segment rotated about a central axis (C-C) of the electromagnetic wave input surface, the tilted line segment being tilted with respect to the central axis (C-C); the tilted line segment and the central axis (C-C) are on the same plane; the central axis (C-C) is in parallel to an extending direction of the optical waveguide; and the central axis (C-C) passes through a projection of the optical waveguide into the electromagnetic wave input surface, characterized in that a tilted angle (α) of the tilted line segment with respect to the central axis (C-C) is determined so that the electromagnetic wave is refracted when transmitting through the electromagnetic wave transmission surface and travels in parallel to the central axis (C-C). a nonlinear crystal that receives excitation light (Lp) having at least two wave length components and outputs an electromagnetic wave having a frequency between 0.01 [THz] and 100 [THz] through the Cherenkov phase matching, the nonlinear crystal having an optical waveguide; a prism that includes an electromagnetic wave input surface which extends parallel to the optical waveguide and which receives the electromagnetic wave from the optical waveguide and an electromagnetic wave transmission surface through which the electromagnetic wave that has entered the electromagnetic wave input surface transmits; and a buffer layer arranged between the prism and the nonlinear crystal, wherein: the prism is attached to the buffer layer; the electromagnetic wave transmission surface includes a rotation surface which is a trajectory of a tilted line segment rotated about a central axis (C-C) of the electromagnetic wave input surface, the tilted line segment being tilted with respect to the central axis (C-C); the tilted line segment and the central axis (C-C) are on the same plane; the central axis (C-C) is in parallel to an extending direction of the optical waveguide; and the central axis (C-C) passes through a projection of the optical waveguide into the electromagnetic wave input surface, the prism is attached to the buffer layer; the electromagnetic wave transmission surface includes a rotation surface which is a trajectory of a tilted line segment rotated about a central axis (C-C) of the electromagnetic wave input surface, the tilted line segment being tilted with respect to the central axis (C-C); the tilted line segment and the central axis (C-C) are on the same plane; the central axis (C-C) is in parallel to an extending direction of the optical waveguide; and the central axis (C-C) passes through a projection of the optical waveguide into the electromagnetic wave input surface, characterized in that a tilted angle (α) of the tilted line segment with respect to the central axis (C-C) is determined so that the electromagnetic wave is refracted when transmitting through the electromagnetic wave transmission surface and travels in parallel to the central axis (C-C).