PURPOSE: To ensure dustproofing by installing a fixed resilient plate and a movable resilient plate at the position of the lower stage of the case apposing the lower aperture of the switch case, which are capable of sealing the opening of the fixed resilient plate while interlocked with motion of a control lever.

CONSTITUTION: A fixed sponge plate 54 and a movable sponge plate 55, which seals the hollow opening part 56 of this fixed sponge plate while interlocked with motion of a control lever 12, are installed in the position of center recess of a switch case 13 on its lower step side mating with an operational shaft insert hole 47. Thus the operational shaft insert hole 47 of the switch case 13 can be sealed only by arranging sponge plates with simple configuration, and therefore the undersurface opening of the switch case can be put in normally closed condition whether the operational lever 12 is in use or not.