PURPOSE: To reduce the delay in the entire circuit and to supply a high oscillating frequency by causing neither turning on/off of a PNP transistor(TR) nor saturation of an NPN transistor.

CONSTITUTION: A charge/discharge capacitor 30, a constant current source 1 giving a charging current, a constant current source 2 discharging the charged electric charge and NPN TRs 18, 19, 20, 21 receiving a voltage of the capacitor 30 as one input form a level detection means. A current switch in the charge/ discharge current path of the capacitor 30 is switched by a level supply means comprising NPN TRs 12, 17 deciding the amplitude of the voltage caused at the capacitor and connected to the other input of the level detection means. Since the on/off of the PNP TR does not exist and the NPN TR is not saturated, then the delay of the entire circuit is reduced to supply higher oscillation frequency.