An actuator comprising: a fixed body (2;2G;2H;2I), comprising: a substrate (10;10G;10H;10I); a plurality of electrodes (11;11G;11H;11I) disposed on a surface of the substrate (10;10G;10H;10I); and an insulating layer (12;12G;12H;12I) disposed on the surface of the substrate (10;10G;10H;10I) and covering the plurality of electrodes (11;11G;11H;11I); an electrically conductive, liquid member, the liquid member disposed on and contacting a surface of the insulating layer (12;12G;12H;12I) forming a contact area between the liquid member and the insulating layer (12;12G;12H;12I); a movable body (3;3A;3B;3C;3G;3H;3I;63) comprising a side surface extending perpendicularly to the insulating layer (12;12G;12H;12I) and a second surface, the second surface being disposed facing the insulating layer (12;12G;12H;12I) without contacting said insulating layer, said movable body contacting the liquid member; a retaining device (20,21,22;30;32,33;34,35) configured to adhere the liquid member to the movable body (3;3A;3B;3C;3G;3H;3I;63); a device configured to apply an electrical potential to each of the plurality of electrodes (11,11G;11H;11I); and a controller configured to control the device to change the potential applied to each of the plurality of electrodes (11;11G;11H;11I) to vary liquid repellency of the insulating layer (12;12G;12H;12I) in response to a difference in the potential applied between each of the plurality of electrodes (11;11G;11H;11I) and the liquid member to change the position, or the position and the size of the contact area between the liquid member and the insulating layer (12;12G;12H;12I), to move the movable body (3;3A;3B;3C;3G;3H;3I;63) relative to the fixed body (2;2G;2H;2I), characterized by the liquid member adhering only to the side surface of the movable body. a fixed body (2;2G;2H;2I), comprising: a substrate (10;10G;10H;10I); a plurality of electrodes (11;11G;11H;11I) disposed on a surface of the substrate (10;10G;10H;10I); and an insulating layer (12;12G;12H;12I) disposed on the surface of the substrate (10;10G;10H;10I) and covering the plurality of electrodes (11;11G;11H;11I); a substrate (10;10G;10H;10I); a plurality of electrodes (11;11G;11H;11I) disposed on a surface of the substrate (10;10G;10H;10I); and an insulating layer (12;12G;12H;12I) disposed on the surface of the substrate (10;10G;10H;10I) and covering the plurality of electrodes (11;11G;11H;11I); an electrically conductive, liquid member, the liquid member disposed on and contacting a surface of the insulating layer (12;12G;12H;12I) forming a contact area between the liquid member and the insulating layer (12;12G;12H;12I); a movable body (3;3A;3B;3C;3G;3H;3I;63) comprising a side surface extending perpendicularly to the insulating layer (12;12G;12H;12I) and a second surface, the second surface being disposed facing the insulating layer (12;12G;12H;12I) without contacting said insulating layer, said movable body contacting the liquid member; a retaining device (20,21,22;30;32,33;34,35) configured to adhere the liquid member to the movable body (3;3A;3B;3C;3G;3H;3I;63); a device configured to apply an electrical potential to each of the plurality of electrodes (11,11G;11H;11I); and a controller configured to control the device to change the potential applied to each of the plurality of electrodes (11;11G;11H;11I) to vary liquid repellency of the insulating layer (12;12G;12H;12I) in response to a difference in the potential applied between each of the plurality of electrodes (11;11G;11H;11I) and the liquid member to change the position, or the position and the size of the contact area between the liquid member and the insulating layer (12;12G;12H;12I), to move the movable body (3;3A;3B;3C;3G;3H;3I;63) relative to the fixed body (2;2G;2H;2I),