PURPOSE: To start oscillation from the potential of a reference voltage by feeding back respectively a current mirror output at the output side of the 2nd and 3rd comparators constituted in a differential pair to a base of the 1st and 2nd transistors (TRs) of the 1st comparator of differential pair constitution.

CONSTITUTION: A resistor R1 and a capacitor C1 are connected between a reference voltage and a base of each TR of the 1st voltage comparator constituted as differential pair by the 1st and 2nd TRs Q1, Q2. An output of the 2nd voltage comparator comprising the 3rd and 4th TRs Q3, Q4 of differential pair constitution and a current mirror circuit connected to the collector is fed back to the base of the 1st TRQ1, and similarly an output of the 3rd voltage comparator of constant current type comprising the current mirror circuit connected to the collector of the 5th and 6th TRs Q5, Q6 is fed back to the base of the 2nd TRQ2. Thus, the oscillation is started from a potential of the reference voltage and oscillated around the said reference voltage.