The nitrogen 1 s near-edge x-ray absorption fine structure (NEXAFS) spectra of the N2 O adsorbed on the Cu(100) surface have been studied by multiple-scattering cluster (MSC) and self-consistent field DV-Xα methods. It is shown that the N2O molecule is adsorbed on the hollow site with the adsorption height h = 3.0±0.1 A. The MSC calculation confirmed by a DV-Xα analysis has revealed the physical cause of the weak feature in the NEXAFS spectra mentioned above, which originates from the 1s core electrons of the centre and terminal nitrogen atoms transiting into the unoccupied σ* orbital of the N2O molecule.