An arm-type support device comprising: a first frame and a second frame; a first arm member that includes a first end and a second end, wherein the first end is supported by the first frame to be pivotal about a first pivot shaft supported by the first frame, and the second end is supported by the second frame to be pivotal about a second pivot shaft supported by the second frame; an actuator configured to move the second frame by pivoting the first arm member about the first frame; and a second arm member that includes a first end and a second end, and extends in parallel with an axis of the first arm member, wherein the first end of the second arm member is supported by the first frame to be pivotal about a third pivot shaft supported by the first frame, and the second end of the second arm member is supported by the second frame to be pivotal about a fourth pivot shaft supported by the second frame, wherein the actuator includes: a driving unit; an actuating rod configured to move in an axial direction of the first arm member in accordance with actuation of the driving unit; and a link member that includes a distal end and a proximal end, wherein the proximal end is pivotally connected to the first frame together with the first end of the second arm member, and the distal end is connected to the actuating rod, the first arm member, the second arm member, the first frame, and the second frame form a parallel link, and the first arm member is hollow and accommodates the actuator, the arm-type support device being characterized in that the first arm member accommodates also the second arm member, and in that the first arm member includes two arm guides extending in the axial direction of the first arm member and being opposed to each other with a space, the second arm member is arranged between the arm guides, and inner surfaces of the arm guides define an opening and the opening is closed by the second arm member. a first frame and a second frame; a first arm member that includes a first end and a second end, wherein the first end is supported by the first frame to be pivotal about a first pivot shaft supported by the first frame, and the second end is supported by the second frame to be pivotal about a second pivot shaft supported by the second frame; an actuator configured to move the second frame by pivoting the first arm member about the first frame; and a second arm member that includes a first end and a second end, and extends in parallel with an axis of the first arm member, wherein the first end of the second arm member is supported by the first frame to be pivotal about a third pivot shaft supported by the first frame, and the second end of the second arm member is supported by the second frame to be pivotal about a fourth pivot shaft supported by the second frame, wherein the actuator includes: a driving unit; an actuating rod configured to move in an axial direction of the first arm member in accordance with actuation of the driving unit; and a link member that includes a distal end and a proximal end, a driving unit; an actuating rod configured to move in an axial direction of the first arm member in accordance with actuation of the driving unit; and a link member that includes a distal end and a proximal end, wherein the proximal end is pivotally connected to the first frame together with the first end of the second arm member, and the distal end is connected to the actuating rod, the first arm member, the second arm member, the first frame, and the second frame form a parallel link, and the first arm member is hollow and accommodates the actuator, the arm-type support device being characterized in that the first arm member accommodates also the second arm member, and in that the first arm member includes two arm guides extending in the axial direction of the first arm member and being opposed to each other with a space, the second arm member is arranged between the arm guides, and inner surfaces of the arm guides define an opening and the opening is closed by the second arm member.