A new scanning tunneling microscope (STM) and its application to surface roughness observation are described. Precision two-dimensional positioning of our STM instrument was achieved with a two-dimensional parallel spring driven by two stacked piezoelectric actuators (PZT), so that the mutual interference effect between x- and y-axis displacements is very small. The PZT for the z-axis displacement and control was mounted on the monolithic parallel spring. Therefore, the mutual interference effect of three-dimensional displacements is negligible. We have applied this STM to observation of surface roughness. A block gauge and a gold thin film evaporated on glass plates are observed at the constant-current mode and the zero bias voltage.