An actuator comprising: a rotary shaft extending in an axial direction; a moving body to move in the axial direction along the rotary shaft in response to a rotation of the rotary shaft upon receiving a rotational drive force; and an actuator main body; a plurality of resonance suppressing mechanisms (6, 9) including a support (61U, 61D, 71U, 71D, 91U, 91D) to support the rotary shaft and a unit (62, 72) to hold the support (61U, 61D, 71U, 71D, 91U, 91D), wherein two resonance suppressing mechanisms are provided, wherein the units (62, 72) are arranged in an arrangement direction orthogonal to the axial direction, a most upstream unit and a most downstream unit are provided as the units, characterized in that each of the units (62, 72) includes a unit main body (621, 721) that is shaped to extend in a moving direction parallel to the axial direction and reciprocally movable with respect to the actuator main body while holding the support (61U, 61D, 71U, 71D, 91U, 91D), a pair of rotating members (622, 623, 722, 723) that are rotatable with respect to the unit main body (621, 721) while being spaced apart in the moving direction, and an endless string (624, 724) mounted between the pair of rotating members (622, 623, 722, 723); in the most upstream unit out of the units (62, 72) in the arrangement direction, a part of the endless string is fixed to the actuator main body at a side upstream of the pair of rotating members (622, 623) in the arrangement direction; in the most downstream unit out of the units in the arrangement direction, a part of the endless string is coupled to the moving body at a side downstream of the pair of rotating members (722,723) in the arrangement direction; in the most upstream unit, a part of the endless string is coupled to the unit main body of the most downstream unit in the arrangement direction at a side downstream of the pair of rotating members (622,623) in the arrangement direction; and in the most downstream unit, a part of the endless string is coupled to the unit main body of the most upstream unit in the arrangement direction at a side upstream of the pair of rotating members (722,723) in the arrangement direction. a rotary shaft extending in an axial direction; a moving body to move in the axial direction along the rotary shaft in response to a rotation of the rotary shaft upon receiving a rotational drive force; and an actuator main body; a plurality of resonance suppressing mechanisms (6, 9) including a support (61U, 61D, 71U, 71D, 91U, 91D) to support the rotary shaft and a unit (62, 72) to hold the support (61U, 61D, 71U, 71D, 91U, 91D), wherein two resonance suppressing mechanisms are provided, wherein the units (62, 72) are arranged in an arrangement direction orthogonal to the axial direction, a most upstream unit and a most downstream unit are provided as the units, characterized in that each of the units (62, 72) includes a unit main body (621, 721) that is shaped to extend in a moving direction parallel to the axial direction and reciprocally movable with respect to the actuator main body while holding the support (61U, 61D, 71U, 71D, 91U, 91D), a pair of rotating members (622, 623, 722, 723) that are rotatable with respect to the unit main body (621, 721) while being spaced apart in the moving direction, and an endless string (624, 724) mounted between the pair of rotating members (622, 623, 722, 723); in the most upstream unit out of the units (62, 72) in the arrangement direction, a part of the endless string is fixed to the actuator main body at a side upstream of the pair of rotating members (622, 623) in the arrangement direction; in the most downstream unit out of the units in the arrangement direction, a part of the endless string is coupled to the moving body at a side downstream of the pair of rotating members (722,723) in the arrangement direction; in the most upstream unit, a part of the endless string is coupled to the unit main body of the most downstream unit in the arrangement direction at a side downstream of the pair of rotating members (622,623) in the arrangement direction; and in the most downstream unit, a part of the endless string is coupled to the unit main body of the most upstream unit in the arrangement direction at a side upstream of the pair of rotating members (722,723) in the arrangement direction.