To stabilize a charging/discharging operation to be stable independently of the fluctuation of a power source voltage by providing a current supply source which is functioned as a constant current source for temp. change and is propotionated to the fluctuation of the power source voltage for the fluctuation of supply voltage and controlling charging/discharging current.

The output of an operational amplifier 201 is transmitted to the gate of NTr 202 and the source terminal output of NTr 202 becomes a negative feedback voltage to the reverse input terminal of the operational amplifier 201. Current I0 permitted to flow in PTr is expressed an expression (number 10) and I0 changes only by relying on the power source voltage VDD regardless of the change of an element characteristic by the temp. change of NTr 202. Then, in a current switch part 103, the charging/discharging current IC1 and IC2 rely on charging/discharging control current which is decided by the output voltage of a current source part 101. Therefore, since the current source part 101 is functioned as the constant current source as against temp. change, a normally stable oscillation frequency is obtained without depending on the change of the element characteristic owing to temp. change.