An electric clamping device, comprising: a main body; a drive motor for providing a driving force; a driving force transfer portion for converting and transferring a magnitude of a driving force of the drive motor; a sliding crank having one side connected to the driving force transfer portion and for converting a rotational motion of the driving force transfer portion to a reciprocating motion; a toggle link having one side connected to the other side of the sliding crank; and a clamp having one side connected to the toggle link and having the other side for clamping or unclamping an object; wherein the driving force transfer portion is formed with engagement of a plurality of gears, and an end gear connected to the sliding crank among the plurality of gears has a speed slower than a rotational speed of the drive motor and a driving force larger than that of the drive motor; wherein the sliding crank comprises: a crank arm having one side connected to the end gear of the driving force transfer portion and coupled apart in a radial direction from the rotation center of the end gear and having the other side coupled to the toggle link, a crank slider formed between one side and the other side of the crank arm and spaced apart from an imaginary straight line connecting one side and the other side of the crank arm, and a guide groove formed in the main body and for providing a movement path of the crank slider; characterized in that the toggle link comprises an elastically deformable link; and the guide groove comprises a curve section formed adjacent to the end gear and a straight section extended from the curve section. a main body; a drive motor for providing a driving force; a driving force transfer portion for converting and transferring a magnitude of a driving force of the drive motor; a sliding crank having one side connected to the driving force transfer portion and for converting a rotational motion of the driving force transfer portion to a reciprocating motion; a toggle link having one side connected to the other side of the sliding crank; and a clamp having one side connected to the toggle link and having the other side for clamping or unclamping an object; wherein the driving force transfer portion is formed with engagement of a plurality of gears, and an end gear connected to the sliding crank among the plurality of gears has a speed slower than a rotational speed of the drive motor and a driving force larger than that of the drive motor; wherein the sliding crank comprises: a crank arm having one side connected to the end gear of the driving force transfer portion and coupled apart in a radial direction from the rotation center of the end gear and having the other side coupled to the toggle link, a crank slider formed between one side and the other side of the crank arm and spaced apart from an imaginary straight line connecting one side and the other side of the crank arm, and a guide groove formed in the main body and for providing a movement path of the crank slider; a crank arm having one side connected to the end gear of the driving force transfer portion and coupled apart in a radial direction from the rotation center of the end gear and having the other side coupled to the toggle link, a crank slider formed between one side and the other side of the crank arm and spaced apart from an imaginary straight line connecting one side and the other side of the crank arm, and a guide groove formed in the main body and for providing a movement path of the crank slider; characterized in that the toggle link comprises an elastically deformable link; and the guide groove comprises a curve section formed adjacent to the end gear and a straight section extended from the curve section.