PURPOSE: To reduce the influence of noise from a reference circuit and to maintain and improve the rise characteristics of the circuit 'by switching the time constant of a low pass filter(LPF) means so as to attain high speed start at the time of starting a reference voltage generating means.

CONSTITUTION: After low pass filtering reference voltage outputted from the reference circuit 1, the LPF impresses the filtered voltage to the non-inverted input terminal of an error amplifier 2. An FET 8 is off at the time of passage and the time constant of the LPF is a product of the resistance value of a resistor 6 and the electrostatic capacity value of a capacitor C. Since the value of the resistor 6 is set up to a value sufficiently larger than the ON resistance of the FET 8, the time constant of the LPF is normally large (i.e., interrupting frequency is low), and at the time of starting the circuit 1, the time constant of the LPF is small (i.e., the cut-off frequency is high).