To provide an electromagnetic wave emission device which emits electromagnetic waves of narrow spectral width.

An electromagnetic wave radiator is heated by a heating mechanism, and an electromagnetic wave is emitted from a radiation surface of the electromagnetic wave radiator. A periodic structure is exposed to the radiation surface. In the periodic structure, a unit structure is arranged periodically in a periodic direction. Each unit structure has a negative permittivity part and a positive permittivity part. A real part of complex relative permittivity of the negative permittivity part is negative. A real part of complex relative permittivity of the positive permittivity part is positive. The negative permittivity part and the positive permittivity part are alternately arranged in the periodic direction. A resonator is formed by each of positive permittivity parts. A period of the periodic structure is a natural multiple of an effective wavelength in an electromagnetic wave radiation surface of resonance frequency of the resonator.