This paper describes the interaction force (adhesive force) based on the atomic force between clean metal (Cu, Ag or Au) surfaces in ultra high vacuum. The interaction force required to separate the contact between the tip and the flat plane is theoretically estimated by the atomic force based on the chemical bond and Hertz's contact theory. In a theoretical analysis, it is assumed that interaction force between clean surfaces can initiate plastic deformation even with zero applied load. This analysis also takes into account of the dislocation density and the size of shear stress field in the contact zone. The interaction force between the tip having radius of 5-25 μm and the flat plane was measured with an electorobalance in ultra high vacuum. At the same time, the contact area was measured by the electrical resistance of contact region. The results of measurement suggested that interaction force alone could initiate plastic deformation. The interfacial energy of Cu was 3.15 J/m2 given by the relation between the measured interaction force and the contact area. The value of measured interfacial energy agreed well with that of atomistically calculated 4.20 J/m2 by considering chemical bonds. Therefore, this suggested that the chemical bond (metallic bond) was induced at the interface.