A high resolution and wide measuring range surface roughness measuring system based on dual servo STM (Scanning Tunneling Microscope) has been developed. STM is very effective method for surface roughness measurement, owing to its ultra-high horizontal and vertical resolution. But STM is not sufficiently useful for various industrial applications, because of the small measuring range especially in the direction vertical. Newly developed dual servo STM has a PZT driven double-compound parallel springs with 60μm travel for coarse mechanism and a PZT for fine mechanism. Both coarse and fine mechanism are controlled simultaneously to get stable tunneling current between measured surface and probe. In this report measuring principle and basic characteristics of the dual servo STM are described. Then it is used to measure surface roughness of machined workpieses and the results are compared with data obtained by a stylus method.