An inertial driving actuator includes a fixing member, a moving element that is fixed to the fixing member and generates a small displacement by extension and contraction, an oscillation substrate that is fixed to the moving element and is moved linearly reciprocally by the small displacement, and a moving body that is moved by reciprocal movement of the oscillation substrate. The moving body has a first electrode. The oscillation substrate has a second electrode, the area of the facing portion of the second electrode and the first electrode changing continuously as the moving body moves. The actuator further includes a frictional force controller that controls a frictional force generated between the oscillation substrate and moving body, and a position detector that detects the position of the moving body on the basis of the electrostatic capacitance of the facing portion of the first electrode and the second electrode.