PURPOSE: To obtain a control voltage having a characteristic in matching with the characteristic of an oscillator and to change the characteristic according to the oscillator by constituting a control voltage generating circuit with a series circuit of many voltage dividing resistors, variable resistors for slope change and upper/lower limit adjustment and changeover switches for said circuits.

CONSTITUTION: A control voltage generating circuit 35 in a channel selection operating section 21 consists of voltage division resistors R1∼R11, variable resistors 38,39 for upper/lower adjustment, a slope change variable resistor 40, and a changeover switch 44 for the voltage division resistors, and further provided with an odd number/even number switching circuit 46 and an adder circuit 51. Thus, in changing over the switch 44 and supplying a control voltage to an oscillator 26, even when the oscillator 26 has a characteristic of chevron shape with respect to an input voltage and the oscillation frequency, since a slope change resistor 40 is connected as shown in figure, the generating circuit 35 can give an oscillator control voltage changing in the relation of a reversed chevron shape to the oscillator 26 according to the switching state of the switch 44. Even when the same resistance is used for the voltage division resistors, a variable resistor is used for the slope change resistor 40 and the voltage of a folding point in the inverse chevron shape characteristic and its higher or lower slope are changed optionally using the variable resistors 38, 39.