An electric clamping device comprising: an output rod inserted in a housing so as to be movable in an axial direction toward a lock side and a release side; a motor attached to the housing; and a decelerator provided beside the output rod, the decelerator configured to transmit rotational motion of the motor to the output rod, wherein the output rod comprises: a tubular power transmission member screw-connected to the decelerator; an output rod main body disposed radially inward of an inner peripheral surface of a cylindrical hole of the power transmission member with a clearance between the output rod main body and the inner peripheral surface; a rotation preventing mechanism configured to prevent relative rotation between the output rod main body and the power transmission member; a lock-side driving mechanism (27, 42) configured to move the output rod main body toward the lock side via the power transmission member; a release-side driving mechanism configured to move the output rod main body toward the release side via the power transmission member; and an output rod guide mechanism configured to guide movement of the output rod main body while preventing co-rotation with the decelerator. an output rod inserted in a housing so as to be movable in an axial direction toward a lock side and a release side; a motor attached to the housing; and a decelerator provided beside the output rod, the decelerator configured to transmit rotational motion of the motor to the output rod, wherein the output rod comprises: a tubular power transmission member screw-connected to the decelerator; an output rod main body disposed radially inward of an inner peripheral surface of a cylindrical hole of the power transmission member with a clearance between the output rod main body and the inner peripheral surface; a rotation preventing mechanism configured to prevent relative rotation between the output rod main body and the power transmission member; a lock-side driving mechanism (27, 42) configured to move the output rod main body toward the lock side via the power transmission member; a release-side driving mechanism configured to move the output rod main body toward the release side via the power transmission member; and an output rod guide mechanism configured to guide movement of the output rod main body while preventing co-rotation with the decelerator. a tubular power transmission member screw-connected to the decelerator; an output rod main body disposed radially inward of an inner peripheral surface of a cylindrical hole of the power transmission member with a clearance between the output rod main body and the inner peripheral surface; a rotation preventing mechanism configured to prevent relative rotation between the output rod main body and the power transmission member; a lock-side driving mechanism (27, 42) configured to move the output rod main body toward the lock side via the power transmission member; a release-side driving mechanism configured to move the output rod main body toward the release side via the power transmission member; and an output rod guide mechanism configured to guide movement of the output rod main body while preventing co-rotation with the decelerator.