plastic knob main body 36 and support pieces 37 projecting downward from the front and back sides thereof and the support holes 37a of the support pieces 37 are engaged with the support lugs 6a of support pieces 6 whereby the main body of the knob is supported by the case 3 so that it can be swung in the direction of arrow a and in the opposite direction a transparent display plate 38 with characters for example 34 auto 34 is attached to the upper end of the knob main body 36 a light guide 39 composed of acrylic resin is formed integrally with and disposed in the knob main body and is provided with a recessed portion 40 corresponding to the above display plate 38 the light guide 39 has protrusion for pressing projections 41 and 42 formed thereon in correspondence to the above return member 29 and the actuating member 34 as shown in fig1 a regulating lug 43 is defined at the center of the pressing projection 41 the right lower surface 41a of the pressing projection 41 is formed so that it has an angle of u03b8 1 u03b8 2 with respect to the upper surface of the knob stopper 7 about the center of rotation the center of the support lug 6a and the support hole 37a and the left lower surface 41b thereof is formed such that it has an angle u03b8 1 note that in the figure the angle u03b8 1 is set to for example 14 u00b0 and the angle u03b8 2 is set to for example 7 u00b0 in this situation the lower surface of the regulating lug 43 in the knob 35 is.