generates the constant voltage through the combination of the transistor tr101 with the zener diode zd10 consequently this constant voltage will be better in temperature compensation and more stable in its characteristics the anode of the zener diode zd10 is connected to ground through a resistor r104 and diodes d101 and d102 the junction point between the resistor r104 and the diode d101 outputs a desired constant voltage the diode d102 is also connected in parallel to a capacitor c100 the constant voltage generating circuit 10 also outputs a predetermined constant voltage from the junction point between the diodes d101 and d102 the gradient detecting unit 11 comprises a differentiating circuit 11a including a capacitor c and a resistor r a transistor tr110 and resistors r111 and r112 namely the amplified signal zs is coupled with the base of the transistor tr110 through the capacitor c the voltage at the junction point between the diodes d101 and d102 in the constant voltage generating circuit 10 is coupled with the base of the transistor tr110 through the resistor r the collector of the npn type transistor tr110 is connected to the emitter of the transistor tr102 in the constant voltage generating circuit 10 through a resistor r111 the emitter of the transistor tr110 is connected to ground through a resistor r112 the collector of the transistor tr110 outputs the processing signal ks for gradient more particularly the base potential in the transistor tr110 varies depending on the output of the differentiating circuit 11a correspondingly the collector current varies to output a gradient dependent voltage signal processing.