An electrodynamic actuator (100, 200, 300, 1100, 1300) for an electrodynamic excitation device, the actuator comprising a cylindrical fixed part having a cylindrical body with a radially extending end surface at one end thereof, the cylindrical body defining a cylindrical hollow part with a center axis; a substantially cylindrical movable frame having an end portion in the center axis direction which is accommodated in the cylindrical hollow part and a protruding end portion in the center axis direction which protrudes outside the radially extending end surface of the cylindrical body, wherein the substantially cylindrical movable frame is driven to reciprocate in the center axis direction; and a movable part support mechanism that supports the movable frame from a lateral side to enable the movable frame to reciprocate along the center axis direction; wherein a plurality of said movable part support mechanisms are arranged around the center axis to have substantially constant intervals therebetween in a circumferential direction and each comprising a guide frame fixed on said radially extending end surface of the cylindrical body to extend in the center axis direction; a rail attached to a side surface of said protruding end portion of the cylindrical movable frame; a plurality of rolling bodies capable of rolling on the rail; and a runner block attached to a center axis extending surface of the guide frame and being movable on the rail by way of the rolling bodies; wherein an entire length of the rail is supported by said protruding end portion of the cylindrical movable frame. a cylindrical fixed part having a cylindrical body with a radially extending end surface at one end thereof, the cylindrical body defining a cylindrical hollow part with a center axis; a substantially cylindrical movable frame having an end portion in the center axis direction which is accommodated in the cylindrical hollow part and a protruding end portion in the center axis direction which protrudes outside the radially extending end surface of the cylindrical body, wherein the substantially cylindrical movable frame is driven to reciprocate in the center axis direction; and a movable part support mechanism that supports the movable frame from a lateral side to enable the movable frame to reciprocate along the center axis direction; wherein a plurality of said movable part support mechanisms are arranged around the center axis to have substantially constant intervals therebetween in a circumferential direction and each comprising a guide frame fixed on said radially extending end surface of the cylindrical body to extend in the center axis direction; a rail attached to a side surface of said protruding end portion of the cylindrical movable frame; a plurality of rolling bodies capable of rolling on the rail; and a runner block attached to a center axis extending surface of the guide frame and being movable on the rail by way of the rolling bodies; a guide frame fixed on said radially extending end surface of the cylindrical body to extend in the center axis direction; a rail attached to a side surface of said protruding end portion of the cylindrical movable frame; a plurality of rolling bodies capable of rolling on the rail; and a runner block attached to a center axis extending surface of the guide frame and being movable on the rail by way of the rolling bodies; wherein an entire length of the rail is supported by said protruding end portion of the cylindrical movable frame.