PURPOSE: To attain minute adjustment for reception channel selection by reducing the turning of a slider of a variable resistor to a channel selection knob into two steps by means of a driving gear, a reduction gear and an outer gear of a display drum.

CONSTITUTION: In turning the channel selection knob 80, the driving gear 70 coupled incorporatedly is turned, and the reduction gear 90 having a gear 93 intermeshing with the driving gear 70 is turned. Moreover, the display drum 10 is turned by being driven by the outer gear 15 intermeshing with the other gear 94 of the reduction gear 90. A slider 41 of a variable resistor 40 coupled incorportedly to the same shaft of the drum 10 is turned and the variable resitor is changed synchronizingly and the device is turned to a desired television channel or a radio frequency. Since the turning of the slider 41 of the variable resistor to the knob 80 is decreased in two steps by the driving gear 70, the reduction gear 90 and the outer gear 15 of the drum 10, minute adjustment is attained.