PURPOSE: To eliminate parts such as damper, etc., with multiple gears to reduce the cost and increase the working efficiency by acting air resistance on a door when it is opened and closed to reduce a rotational speed of it when the door is opened.

CONSTITUTION: A lock is released in a closed condition, and an opening and closing door 26 of an operation panel is rotated in the direction of arrow B around a rotational shaft 25. At the same time, a hinged section 30 is rotated around the rotational shaft 25 while deforming elastically. Also a swing section 27 pushes an inserting section 26 into an inserting hole 24 of a cabinet 21 through a hinged section 31 while swinging. In this case, a cross-sectional area of a vent hole 23 in the inserting hole 24 is made smaller than that of the inserting section 28, and the amount of air discharged to the outside of the inserting hole 24 is reduced. Also air is compressed to act a force on the inserting section 28 to restrict the advancement of it by damper action. Then a rotational speed of the operation panel opening and closing door 7 is reduced when it is opened. Thus parts such as a damper, etc., is not required, and screwing work for parts such as a damper, etc., is abolished to increase the working efficiency.