A capped multimalled carbon nanotube with clean surface gives field emission patterns consisting of six pentagonal rings which correspond to pentagons located at the tip end. One or a few bright streaks are also observed at the boundaries of neighboring pentagons. The spacing of streaks is inversely proportional to the square root of the accelerating voltage. Namely, the spacing changes with the wavelength of emitted electrons according to Young's interference equation. The visibility of streaks increased with the accelerating voltage, which can be explained in terms of a concept of a virtual source size. These experimental results suggest that the streaks are no more than Young's interference fringes for which the adjacent pentagons behave as double slits. 2004 American Vacuum Society.