The emission properties of the pyramidal-shaped diamond after hydrogen and oxygen surface treatments were discussed. There was a shift in C1s binding energy peak in the x-ray photoelectron spectrum due to the surface treatments. The lowest turn-on voltage in the emission current versus anode voltage characteristics is observed after the hydrogen treatment. The emission barrier height ratios against the as-prepared surface are found to be 0.68 for hydrogen treated and 2.1 for oxygen treated surfaces, respectively, from the slopes of the Fowler-Nordheim characteristics. The change in the barrier height is speculated to be explained by the dipole formed at the diamond surface. The emission stability is also confirmed, and this remarkable feature was obtained for a hydrogen-treated surface.