An auxiliary thrust device includes a membrane, a carrier tube, and a drive cylinder. First and second insertion holes into which first and second torque wires are inserted are formed in a wire sheath. First and second gears are fixed to tip portions of the torque wires, which protrudes from a tip of the wire sheath, respectively. The first gear fixed to the first torque wire meshes with a spur gear portion of the drive cylinder, and the second gear connected to the second torque wire meshes with the first gear. Since the respective torque wires are inserted into one wire sheath and are bent in the same shape, a frictional force generated between the first torque wire and the inner surface of the wire sheath is substantially the same as that generated between the second torque wire and the inner surface of the wire sheath.
