The surface of the layered chalcogenide ReS2 was examined by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), and the structure of ReS2 was determined by single crystal X-ray diffraction measurements. The observed atomic-resolution AFM and STM images were analyzed by calculating the total and partial electron density distributions [p(r(0)) and p(r(0),rho(f)), respectively] of a single ReS2 layer taken from the bulk crystal structure. Our results show that the STM images are associated with the surface S atoms. The p(r(0),rho(f)) plots of the two tunneling processes differ in topography from the p(r(0)) plot so that the surface atomic structure cannot be unambiguously deduced from the analysis of atomic-resolution STM images alone. Calculations of the p(r(0)) and p(r(0),rho(f)) plots are essential for properly interpreting the atomic-resolution AFM and STM images.