A clamp device for clamping a workpiece (W1, W2) between a plurality of clamp arms , comprising: a clamp body ; a plurality of clamp arms supported movably with respect to the clamp body ; a driving unit having a displacement body for linear reciprocating motion and mounted on the clamp body ; and a driving force transmission mechanism configured to transmit a driving force from the driving unit to each of the clamp arms , wherein the driving force transmission mechanism is configured to convert the linear motion of the displacement body into a first motion for moving and rotating the plurality of clamp arms in a direction toward or away from each other, and into a second motion for translating the plurality of clamp arms in a direction toward or away from each other in a state where gripping surfaces of the respective clamp arms to contact the workpiece (W1, W2) are in parallel, characterized in that the driving force transmission mechanism comprises: a movable part provided on the displacement body , a first cam hole being formed in the movable part ; a fixed part provided on the clamp body , a second cam hole being formed in the fixed part ; a first shaft and a second shaft provided with respect to each of the clamp arms ; a first roller rotatably provided on the first shaft and movable in the first cam hole ; a second roller rotatably provided on the first shaft and movable in the second cam hole ; and a third roller rotatably provided on the second shaft and movable in the second cam hole , wherein the movable part and the fixed part are arranged such that the first cam hole and the second cam hole at least partially overlap each other in plan view. a clamp body ; a plurality of clamp arms supported movably with respect to the clamp body ; a driving unit having a displacement body for linear reciprocating motion and mounted on the clamp body ; and a driving force transmission mechanism configured to transmit a driving force from the driving unit to each of the clamp arms , wherein the driving force transmission mechanism is configured to convert the linear motion of the displacement body into a first motion for moving and rotating the plurality of clamp arms in a direction toward or away from each other, and into a second motion for translating the plurality of clamp arms in a direction toward or away from each other in a state where gripping surfaces of the respective clamp arms to contact the workpiece (W1, W2) are in parallel, characterized in that the driving force transmission mechanism comprises: a movable part provided on the displacement body , a first cam hole being formed in the movable part ; a fixed part provided on the clamp body , a second cam hole being formed in the fixed part ; a first shaft and a second shaft provided with respect to each of the clamp arms ; a first roller rotatably provided on the first shaft and movable in the first cam hole ; a second roller rotatably provided on the first shaft and movable in the second cam hole ; and a third roller rotatably provided on the second shaft and movable in the second cam hole , wherein the movable part and the fixed part are arranged such that the first cam hole and the second cam hole at least partially overlap each other in plan view. a movable part provided on the displacement body , a first cam hole being formed in the movable part ; a fixed part provided on the clamp body , a second cam hole being formed in the fixed part ; a first shaft and a second shaft provided with respect to each of the clamp arms ; a first roller rotatably provided on the first shaft and movable in the first cam hole ; a second roller rotatably provided on the first shaft and movable in the second cam hole ; and a third roller rotatably provided on the second shaft and movable in the second cam hole , wherein the movable part and the fixed part are arranged such that the first cam hole and the second cam hole at least partially overlap each other in plan view. <EOS>