The internal structure of the prestellar core G208.68-19.02-N2 (G208-N2) in the Orion Molecular Cloud 3 (OMC-3) region has been studied with the Atacama Large Millimeter/submillimeter Array. The dust continuum emission revealed a filamentary structure with a length of similar to 5000 au and an average H2 volume density of similar to 6 x 107 cm-3. At the tip of this filamentary structure, there is a compact object, which we call a nucleus, with a radius of similar to 150-200 au and a mass of similar to 0.1 M circle dot. The nucleus has a central density of similar to 2 x 109 cm-3 with a radial density profile of r -1.87 +/- 0.11. The density scaling of the nucleus is similar to 3.7 times higher than that of the singular isothermal sphere (SIS). This as well as the very low virial parameter of 0.39 suggests that the gravity is dominant over the pressure everywhere in the nucleus. However, there is no sign of CO outflow localized to this nucleus. The filamentary structure is traced by the N2D+ 3-2 emission, but not by the C18O 2-1 emission, implying the significant CO depletion due to high density and cold temperature. Toward the nucleus, the N2D+ also shows the signature of depletion. This could imply either the depletion of the parent molecule, N2, or the presence of the embedded very-low luminosity central source that could sublimate the CO in the very small area. The nucleus in G208-N2 is considered to be a prestellar core on the verge of first hydrostatic core (FHSC) formation or a candidate for the FHSC.