A scanning tunneling microscope (STM) is a kind of micromachine, from an instrumentational and functional point of view. In this paper, the present and future status of key technologies of STM instrumentation and miniaturization are discussed after presenting the principle of STM operation. Application of STM functions to nanometer-scale fabrication and ultimate modification of surfaces on an atomic or molecular scale will pave the way for future electron devices and the synthesis of new materials.