An actuator according to an aspect of the present invention includes: a driving body including a plurality of conductive grains, a chamber configured to confine the plurality of conductive grains, and two or more electrodes disposed on a surface of the chamber; and a controller configured to obtain, through the two or more electrodes, a change in an electric signal, in response to a load applied to the chamber, and to adjust the load applied to the chamber based on the change in the electric signal.