PURPOSE: To enhance the performance of a tuner, by increasing the minimum value of the tuning voltage of a tuner using a variable capacity diode in order to secure a reception of the minimum channel of a comparative high tuning voltage for the tuner side.

CONSTITUTION: The resistance R6 is connected between the power supply line 2 and the connection point (a) between the temperature compensating transistor TR1 and the constant current transistor TR2, and thus the lower limit value is set for the tuning voltage by the resistance R6. In other words, the voltage higher than nearly 0V is secured at the output terminal 3 by securing a flow of the current to the transistor TR2 through the resistance R6 although the voltage supplied to the base of the transistor TR1 becomes almost 0V by the variable resistors VR1∼ VRn. In this case, a comparatively high and specific value is selected for the resistance R6, and as a result the voltage can be set at a certain value (such as 1.25V or the like).