A subassembly includes an intermediate knob serving as a first knob rotatably fitted to and supported by a middle serving as a fixing portion, a first spring and a first ball for giving a detent feeling upon a rotary movement between the middle serving as the fixing portion and the intermediate knob, a distal end knob serving as a second knob rotatably fitted to and supported by the middle serving as the fixing portion, and a second spring and a second ball for giving a detent feeling upon a rotary movement between the middle serving as the fixing portion and the distal end knob. In such a subassembly, the intermediate knob, the first spring and the first ball, and the distal end knob, the second spring and the second ball are integrally assembled as a subassembly.