To prevent relative racing of a cylindrical part of a rotary operating shaft and a shaft part of an operating knob, besides suppressing the occurrence of misalignment at an interference fit part of both parts, when connecting both parts by interference fit.

When the cylindrical part 120 of the rotary operating shaft 130 and the shaft part 110 of the operating knob 2 are connected by interference fit to make increase/decrease adjustment of the fitting allowance of both parts, expanding slots 121 are provided at four circumferential equal angle parts of the cylindrical part 120. One expanding slot 121 is used as a key slot to which a key part 112 is fitted. The height position of the operating knob 2 to an upper plate part 11 of a casing 1 of a projector is adjusted by making the increase/decrease adjustment of the fitting allowance of the cylindrical part 120 and shaft part 110.