We report the atomic-resolution imaging of an individual single-walled carbon nanotube and quantitative measurements of forces above specific atomic sites by dynamic force microscopy and three-dimensional force field spectroscopy at low temperatures. The detailed structure, i.e., the pair of indices (n, m) corresponding to a chiral angle phi and diameter d, is derived from atomic resolution images. Through the evaluation of short-range forces, the chemical reactivity of nanotube surface is found to be very weak when the interatomic short-range van der Waals forces are dominant.