In order to evaluate the damage caused by a single MeV ion impact, we prepared highly oriented pyrolytic graphite specimens, each implanted with 3.1 MeV Au, Ag, Cu and Si ions at a dose of 2.3×1011 cm-2 (2300 μm-2). We then observed specimens by using friction force microscope, and found round regions caused by single-ion impacts on the implanted surface. The frictional force between the surface and the silicon-nitride tip increased in disordered regions. The number density of the regions differed at individual ion-implanted surface, and was about 1000 μm-2 at the Au-implanted surface, 880 μm-2 at the Ag-implanted surface, 372 μm-2 at the Cu-implanted surface, and 44 μπτ2 at the Si-implanted surface. We calculated the electronic stopping power and the probability of knock-on atom generation by the nuclear collision to determine which process affected the density. We found that the difference in the number density was closely related to that of nuclear collisions.