Abstract: An object of the present invention is to improve the manipulating property of a rotary knob device. According to the present invention, a variable resistor and switch has an inner unrotatable shaft, and an outer rotatable shaft. A first manipulation member having a light guide portion, a light bending portion and a luminous portion is coupled to the inner shaft. A sign indicative of the method of manipulation of the resistor and switch, and a sign indicative of the function thereof are provided on the luminous portion. The luminous portion is illuminated to make the signs clearly visible. The signs provided on the first manipulation member fitted on the inner unrotatable shaft are illuminated with the luminous portion of the member so that the signs are shown at a high luminance to improve the manipulating property of the knob device.