We have measured transmission properties of a composite structure consisting of nano-rods on a long (ay=300 micron) nano gap (70 nm) on Au film in broad frequency range of 0.1 THz to 1.0 THz using THz time-domain spectroscopy. The normalized transmittance with no nano-bridge or nano-rod structure in the middle shows a half-wavelength resonance: the resonance frequency is ∼c/(2nay) where n is the index of refraction of the substrate. The nano-size bridge at the center of the nano gap gives changes the resonance characteristics profoundly, because in essence, the length a y now halves. Mostly the same resonance-changing behavior is expected with a nano-rod structure fabricated by Pt-deposition method using a focused ion beam (FIB). This small rod also acts as a bridge dividing the length of the rectangle. The structure dependent resonance allows to detect nano-size particles and to tailor resonance characteristics with feature sizes of λ/10,000.