<p>A waveguide element (10) comprising a photonic crystal (2) which is a core exhibiting unidirectional periodicity of refractive index and having a bottom face perpendicular to the periodic direction of refractive index and an incoming side inclined surface (2a) and an outgoing side inclined surface (2b) inclining against the bottom face, a light input portion (3), and a light output portion (4). The light input portion (3) lets the light into the photonic crystal (2) through the bottom face. The light entered into the photonic crystal (2) is reflected off the incoming side inclined surface (2a) and propagation light is generated in the photonic crystal (2) by a band on the Brillouin zone boundary. The propagation light is reflected off the outgoing side inclined surface (2b) and the light exits from the bottom face of the photonic crystal (2). The outgoing light from the photonic crystal (2) is led to the light output portion (4). Fabrication is facilitated because of simple structure, and a small waveguide element suitable for vertical coupling can be provided.</p>
