We numerically investigated the characteristics of contact force, adhesion force, and contact stiffness between a smooth contact pad and a small rough surface, such as a current magnetic disk surface. The computer-generated asperity had an isotropic Gaussian distribution with a small asperity height and high asperity density. We took asperity contact, bulk deformation, and meniscus force of a lubricant layer at contacting asperity into consideration in the calculations. We evaluated the effects of asperity density, contact pad area, asperity radius, root mean square (RMS) asperity height, and lubricant thickness on external and internal contact forces, adhesion force, and contact stiffness as a function of the separation between the contact pad and disk in both approaching and separating processes. We found that contact and adhesion force tend to change suddenly at the start and end of contact and exhibits hysteresis in the approaching and separating processes when asperity density becomes large and RMS asperity height becomes small comparable with current head sliders and magnetic disks. We also found that contact stiffness is governed by bulk deformation and that the contact stiffness and adhesion force can be regarded as constant during contact when the asperity density increases, the RMS asperity height decreases, and the contact area increases.