Triboluminescence spectra were measured by means of pin-on-disk method for several samples of natural diamond and a synthetic quartz disk in Ne or N₂ gas at pressures between 10 and 10⁵ Pa. At the gas pressure between 10 and 1000 Pa, a blue luminescence was observed besides the gas discharge luminescence due to triboelectricity. The spectrum of cathode-ray luminescence, which was measured by electron bombardment on the same diamond sample, was identical with that of the blue luminescence. The gas pressure dependence of the blue luminescence intensity also supports the model that the blue luminescence was induced by electron impact on the diamond surface in the gas discharge.