Using a recently developed atomic force microscopy (AFM) simulator ACCESS (AFM simulation Code for Calculating and Evaluating Surface Structures), effects of tip apex size on AFM images were examined. A metal tip-metal sample system consisting of iron tip and copper sample was employed as a model system. Structures with half the surface periodicity, which have been observed in actual AFM measurements, were observed at certain tip apex registries. Conditions for their appearances were examined.