One feature of the invention is to support a wiring structure on a side surface of an actuator arm used in a magnetic disk device so as not to allow fluttering to occur. In one embodiment, a wire support member 102a used in a magnetic disk device includes a protruding wall 108a provided with an opposing surface facing a wiring structure 90a and protruding in a width direction, and a protruding wall 110a provided with an opposing surface facing the wiring structure 90a and protruding in a width direction. The wire support member 102a is provided with a fixing area for accommodating the wiring structure between the opposing surface of the protruding wall 108a and the opposing surface of the protruding wall 110a. The wire support member 102a is further provided with an open area adjoining the fixing area at a longitudinal end portion of the protruding wall and includes protruding walls 328, 330, 332 each having an opposing surface facing the wiring structure.