PURPOSE: To perform an automatic channel selection by giving a short circuit between the time axis and the desired channel selection position where the channel axis crosses, deciding one side of the bridge balanced circuit and then detecting the unbalance to actuate the channel selection mechanism.

CONSTITUTION: Both the desired time and channel are set for axes M1∼Mn and channel axes CH1∼CHn with short circuit given via short element 8. At the prescribed time, mobile contact 6 shifts by timer 1 to select the prescribed channel. At the same time, intermittent action switch 4 is turned on to switch transistor TR4 on. Thus the bridge becomes unbalanced, and then bridge unbalance detection circuit (diodes D1 and D2 plus resistances R1 and R2) drives transistors TR1, TR2 and TR3 each and then turns channel selection driving motor 9 to perform switching of the channels. The motor stops when the bridge is balanced.