An actuator comprising: a motor having a rotation shaft; an output shaft which outputs rotation of the rotation shaft; a speed reduction mechanism provided between the rotation shaft and the output shaft; and a case in which the motor and the speed reduction mechanism are accommodated, the case having: an accommodating portion in which the motor is accommodated; a support portion provided and arranged side by side with the accommodating portion in a direction crossing an axial direction of the accommodating portion, the support portion supporting the output shaft, a length of the support portion in an axial direction being shorter than a length of the accommodating portion in the axial direction; a convex portion provided to the support portion and located on the opposite side of the support portion from the accommodating portion, the convex portion protruding in a direction crossing the output shaft; and a weld line provided to the accommodating portion and located on the opposite side of the support portion from the support portion, characterized by a reinforcing rib provided to a portion in which the weld line is formed, the reinforcing rib protruding from the accommodating portion to outside, wherein the convex portion is formed by an inlet portion for molten material in upper and lower molds (70, 60), and the weld line is formed by the merger of molten material. a motor having a rotation shaft; an output shaft which outputs rotation of the rotation shaft; a speed reduction mechanism provided between the rotation shaft and the output shaft; and a case in which the motor and the speed reduction mechanism are accommodated, the case having: an accommodating portion in which the motor is accommodated; a support portion provided and arranged side by side with the accommodating portion in a direction crossing an axial direction of the accommodating portion, the support portion supporting the output shaft, a length of the support portion in an axial direction being shorter than a length of the accommodating portion in the axial direction; a convex portion provided to the support portion and located on the opposite side of the support portion from the accommodating portion, the convex portion protruding in a direction crossing the output shaft; and a weld line provided to the accommodating portion and located on the opposite side of the support portion from the support portion, characterized by a reinforcing rib provided to a portion in which the weld line is formed, the reinforcing rib protruding from the accommodating portion to outside, wherein the convex portion is formed by an inlet portion for molten material in upper and lower molds (70, 60), and the weld line is formed by the merger of molten material. an accommodating portion in which the motor is accommodated; a support portion provided and arranged side by side with the accommodating portion in a direction crossing an axial direction of the accommodating portion, the support portion supporting the output shaft, a length of the support portion in an axial direction being shorter than a length of the accommodating portion in the axial direction; a convex portion provided to the support portion and located on the opposite side of the support portion from the accommodating portion, the convex portion protruding in a direction crossing the output shaft; and a weld line provided to the accommodating portion and located on the opposite side of the support portion from the support portion, characterized by a reinforcing rib provided to a portion in which the weld line is formed, the reinforcing rib protruding from the accommodating portion to outside, wherein the convex portion is formed by an inlet portion for molten material in upper and lower molds (70, 60), and the weld line is formed by the merger of molten material.