Disclosed is a surface plasmon optic device that has a periodic array of apertures in a dielectric substrate and a metal film formed on the dielectric substrate and emits light from metal-air interface. The surface plasmon optic device includes a surface plasmon generating apparatus, a surface plasmon detecting apparatus, a surface plasmon controlling apparatus, an etching apparatus, etc. if a metal diffraction grating is disposed on the metal film having a well-defined interface, propagation of the surface plasmon can be efficiently reflected, divided and controlled. Further, radiating surface plasmon having a half period of a lattice constant formed at air-metal (1, 0) can be preserved at a distance of at least a few micron.