An electrodynamic actuator 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 . <EOS>