We have observed the cleaved NiO(100) surface by means of the UHV non-contact atomic force microscopy (NC-AFM). Atomically resolved NC-AFM images of NiO(100)-cleaved surface has successfully obtained with atomically distinguishable defects at room temperature. The distance of the observed periodic protrusions is about 4.2 Angstrom and the periodicity corresponds to that of sublattice of NiO single crystal.