In order to elucidate the difference of the mechanisms of imaging between scanning tunneling microscopy (STM) and non-contact atomic force microscopy (NC-AFM), the atomic structure and local physical properties of SrTiO₃(100) surface were studied by using STM and NC-AFM. We theoretically simulated a model cluster with first-principles total energy calculation. Calculated density of states (DOS), work function, images for STM and NC-AFM were in good agreement with experimental data.