An inertial drive actuator includes a fixed member, a displacement generating mechanism which is connected to the fixed member, and which generates a minute displacement in a first direction and a second direction, a vibration substrate which reciprocates by the minute displacement generated by the displacement generating mechanism, a mobile object which is disposed on the vibration substrate, and which is movable by inertia, a driving mechanism which is connected to the mobile object, and which controls a frictional force between the mobile object and the vibration substrate by making an electromagnetic force to act in the mobile object by applying a current, a detecting electrode having a position detection function, which is disposed on a flat surface of the vibration substrate, to be facing the mobile object via an insulating body layer, and which is formed such that, an area face-to-face thereof with the mobile object either increases continuously or decreases continuously with the movement of the mobile object, and a position detecting mechanism which detects a position of the mobile object by detecting an electrostatic capacitance generated between the mobile object and the detecting electrode.