A clamp device for clamping a workpiece (W1, W2) between a plurality of clamp arms (16a, 16b), comprising: a clamp body; a plurality of clamp arms (16a, 16b) 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 (16a, 16b), 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 (16a, 16b) in a direction toward or away from each other, and into a second motion for translating the plurality of clamp arms (16a, 16b) in a direction toward or away from each other in a state where gripping surfaces (66a, 66b) of the respective clamp arms (16a, 16b) to contact the workpiece (W1, W2) are in parallel, characterized in that the driving force transmission mechanism comprises: a movable part (68, 70) provided on the displacement body, a first cam hole (88a, 88b) being formed in the movable part (68, 70); a fixed part (76, 78) provided on the clamp body, a second cam hole (106a, 106b) being formed in the fixed part (76, 78); a first shaft (112a, 112b) and a second shaft (114a, 114b) provided with respect to each of the clamp arms (16a, 16b); a first roller (116a, 116b) rotatably provided on the first shaft (112a, 112b) and movable in the first cam hole (88a, 88b); a second roller (118a, 118b) rotatably provided on the first shaft (112a, 112b) and movable in the second cam hole (106a, 106b); and a third roller (120a, 120b) rotatably provided on the second shaft (114a, 114b) and movable in the second cam hole (106a, 106b), wherein the movable part (68, 70) and the fixed part (76, 78) are arranged such that the first cam hole (88a, 88b) and the second cam hole (106a, 106b) at least partially overlap each other in plan view. a clamp body; a plurality of clamp arms (16a, 16b) 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 (16a, 16b), 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 (16a, 16b) in a direction toward or away from each other, and into a second motion for translating the plurality of clamp arms (16a, 16b) in a direction toward or away from each other in a state where gripping surfaces (66a, 66b) of the respective clamp arms (16a, 16b) to contact the workpiece (W1, W2) are in parallel, characterized in that the driving force transmission mechanism comprises: a movable part (68, 70) provided on the displacement body, a first cam hole (88a, 88b) being formed in the movable part (68, 70); a fixed part (76, 78) provided on the clamp body, a second cam hole (106a, 106b) being formed in the fixed part (76, 78); a first shaft (112a, 112b) and a second shaft (114a, 114b) provided with respect to each of the clamp arms (16a, 16b); a first roller (116a, 116b) rotatably provided on the first shaft (112a, 112b) and movable in the first cam hole (88a, 88b); a second roller (118a, 118b) rotatably provided on the first shaft (112a, 112b) and movable in the second cam hole (106a, 106b); and a third roller (120a, 120b) rotatably provided on the second shaft (114a, 114b) and movable in the second cam hole (106a, 106b), wherein the movable part (68, 70) and the fixed part (76, 78) are arranged such that the first cam hole (88a, 88b) and the second cam hole (106a, 106b) at least partially overlap each other in plan view. a movable part (68, 70) provided on the displacement body, a first cam hole (88a, 88b) being formed in the movable part (68, 70); a fixed part (76, 78) provided on the clamp body, a second cam hole (106a, 106b) being formed in the fixed part (76, 78); a first shaft (112a, 112b) and a second shaft (114a, 114b) provided with respect to each of the clamp arms (16a, 16b); a first roller (116a, 116b) rotatably provided on the first shaft (112a, 112b) and movable in the first cam hole (88a, 88b); a second roller (118a, 118b) rotatably provided on the first shaft (112a, 112b) and movable in the second cam hole (106a, 106b); and a third roller (120a, 120b) rotatably provided on the second shaft (114a, 114b) and movable in the second cam hole (106a, 106b), wherein the movable part (68, 70) and the fixed part (76, 78) are arranged such that the first cam hole (88a, 88b) and the second cam hole (106a, 106b) at least partially overlap each other in plan view.