B 1s and Si 2s core levels, which correspond to the XPS spectra within a frozen-orbital approximation, are calculated for various defect models containing B atoms. The calculation is based on the density functional theory and the core levels are obtained using the ultrasoft pseudopotential and its multi-reference technique. The core level dependence on the cell size is evaluated with 64, 216, and 512 Si cubic supercell. In the 216 and 512 cell, the accuracy is about 0.1 eV. The core levels are fairly different for the boron atoms even with the same coordination number. For example, the 〈001〉 split B2 and the 3-fold B with hydrogen terminated vacancy both contains the 3-folded B atoms but shows large difference by 0.7 eV.