We have investigated the on-orbit properties of the spectroscopic data taken with NIR channel of the Infrared Camera (IRC) onboard AKARI during the phases 1, 2 and 3. We have determined the boundary shape of the aperture mask of NIR channel by using the spectroscopic data of uniform zodiacal background emission. The information on the aperture mask shape is indispensable in modeling and subtracting the spectroscopic background patterns made by the diffuse background emission such as zodiacal emission and the Galactic cirrus emission. We also have examined the wavelength dependency on the profile of the point spread function and its effect on the spectroscopic data. The obtained information is useful, for example, in reducing the spectroscopic data of a point source badly affected by bad pixels and in decomposing the overlapping spectra of sources that are aligned in the dispersion direction with a small offset the cross dispersion direction. In this paper, we summarize the supplementary knowledge that will be useful for the advanced data reduction procedures of NIR spectroscopic datasets.