PURPOSE: To produce easily an IC by adding a transistor to a level supply means for formation of a constant current source and therefore reducing the resistance value for decision of a low potential level of oscillation output.

CONSTITUTION: A current mirror connection is secured between transistors TR 6 and TR 1.Thus a fixed current source is formed for supply a constant current to a resistance 17. The resistance 17 functions to decide a low potential level of oscillation output. Thus the collector current of the TR 6 flows to the resistance 17 in addition to the base currents of TR 10 and TR11. In other words, the resistance value of the resistance 17 can be reduced by an amount equivalent to the collector current amount of the TR 6. Because the value of the resistance 17 can be reduced down a corresponding level by the capacity of the TR 6, an easy production of an IC can be attained.