For long wave length infrared transmission, a surface plasmonic device, having the periodic subwavelength metal hole array on Si substrate, was fabricated using photo-lithography and electron beam evaporation. The maximum transmitted wavelength was adjustable arbitrarily as a function of the period hole arrays. The maximum transmittance was measured 70.3% at 15.4 μm with a plasmonic device composed of a pitch of 5 μm and hole arrays of 3 μm. When the hole size became larger than a half pitch of the hole array, the transmitted infrared spectrum was split into two peaks. The surface plasmon mode of the six degenerated (1,0) Ag/Si was split from three to five modes depending on the incident beam angle. The blue and red wavelength shifts were measured at the same time.