PURPOSE: To directly operate the knob of a flash valve, facilitate fitting, and reduce the cost.

CONSTITUTION: A motor 16 is stored in the housing 7 of a cleaning device 6, and a small bevel gear 18 is fitted to the rotary shaft of the motor 16. A large bevel gear 19 is supported in the housing 7 unmovably in the axial direction so that its axis coincides with the axis of the knob 5 of a flash valve 4. The small bevel gear 18 is meshed with the large bevel gear 19. A hole is formed at the center of the large bevel gear 19, and a male screw shaft 21 is relatively unmovably stored in the hole. A clip 20 having a coupling section is integrally rotatably fixed to the large bevel gear 19. The male screw shaft 21 is screwed to the coupling section of the clip 20. The tip of the male screw shaft 21 is connected to the knob 5. When the motor 16 is driven forward, the male screw shaft 21 is advanced, and the knob 5 is submerged.