PURPOSE: To reduce friction and improve screw efficiency by rotating a rotary member in its peripheral direction so as to revolve rollers in the same direction as that of the rotary member while rotating the rollers around their own axes, thereby letting the rollers interfere with the slant face of the thread ridge of the trapezoidal male screw thread to elevated a screw rod.

CONSTITUTION: A reciprocating device 6 is provided with line pairs formed of a trapezoidal male thread part 2A formed on a screw rod 2 and truncated conical rollers 7 brought into line contact with the inclined face of the thread ridge 2a of the trapezoidal male screw thread part 2A. The rollers 7 are rotatably supported on roller bearings 8 fitted to a rotary member 10. The rotary member 10 is rotated by operating a worm 11, and in association with this rotation, the above-mentioned rollers 7 are revolved in the same direction as that of the rotary member 10 while being self-rotated, and interfere with the slant face of the thread ridge 2a to elevated the screw rod 2 and thereby to switch a regulating door 1. Because of the line pair structure formed of the trapezoidal male thread part 2A and the rollers 7 brought into line contact with the inclined part of the thread ridge 2a of the male thread part 2A, frictional resistance is small, screw efficiency is improved, and the generation of screw sound is prevented.