by reducing the resistance r 5 so as to be lower than the resistance r 6 moreover an excellent regulator or reference source which can operate in the condition of lower feed voltage lower than 1 2 volts can be provided easily fig2 shows a second embodiment of the present invention in fig2 the collector of the transistor 7 is connected through a resistor 17 to the output feed line b the noninverting input terminal 11a of the voltage comparator 11 is connected to the collector of the transistor 7 and an output control transistor 18 of reverse conductive type is employed instead of the output control transistor 12 the voltage regulator shown in fig2 operates certainly in the condition of lower feed voltage compared with the prototype shown in fig1 fig3 shows a third embodiment of the present invention the collector of the transistor 7 is connected to the base of a transistor 19 and the collector of a transistor 20 the emitter of the transistor 19 is connected to the base of the transistor 20 and the collector of the transistor 19 is connected to the negative feed line c the emitter of the transistor 20 is connected through a resistor 21 to the output feed line b the base of a transistor 22 is connected to the base of the transistor 20 the emitter of the transistor 22 is connected through a resistor 23 to the output feed line b and the collector of the transistor 22 is connected to the collector of the transistor 3 the base of a transistor 24 is connected to the base of the transistor 20 the emitter of the.