True atomic resolution imaging of the cleaved semi-insulating InP(110) surface was demonstrated using an ultrahigh vacuum atomic force microscope (AFM) in noncontact mode. The force gradient acting on the tip was detected by the frequency modulation method. The rectangular lattice could be clearly observed. The image contrast suddenly changed during the scan, which suggests that the noncontact AFM imaging is performed under the condition of nearly monoatomic tip-sample force interaction. Atomic defects have been clearly and reproducibly observed. These results suggest that noncontact AFM has the potential for true atomic-scale lateral resolution and is quite effective for atomic surface structure analysis in real space.