PURPOSE: To output a power restoration signal when the generator is normal and the power is restored, by inputting an output signal of a processing circuit inputting power failure to a window comparator, rectifying an oscillating output of the comparator and applying it to a delay circuit to reduce the delay time at failure.

CONSTITUTION: A DC signal from a power input terminal 1 is integrated by an integrating circuit 2 of a power restoration signal generator and its output signal is inputted to the window comparator 3. The window of the comparator 3 detects the level of an input signal, and a transmission output is generated when the level is over or below the indow and the circuit is failed. The oscillating output of the comparator 3 is rectified by a rectifier circuit 4, an output of the rectifier circuit 4 is inputted to a delay circuit 5 to reduce the delay time at failure from the delay circuit 5, thereby generating a pulse signal. Only when the power failure restoring signal generator is normal and the power supply is restored, the power failure restoring signal is outputted.