A driving method suitable for a micro mechanism is introduced. It utilizes friction and inertial force caused by rapid deformations of piezoelectric elements. A one-dimensional linear positioner using this mechanism consists of one main object put on a guiding surface, a piezo, and a weight. The weight is connected to one end of the main object via the piezo. By controlling rapid extension or contraction of the piezo, it can make step-like movements of several nanometers up to ten micrometers bidirectionally against friction. By repeating this step movement, it can move for a long distance. Using this mechanism, two types of joints for micro robot arm are developed. One is a simple rotating joint with an arm of 5 cm, and the other is a three-degree-of-freedom (DOF) joint with an 8 cm arm. Minimum step movements of the two joints were smaller than 0.1 mu m and maximum velocities were larger than 2 mm/sec at the end of the arm. Combining two joints, a four-DOF micro robot arm was developed.<<ETX>>