To provide a backup circuit enabling backup for prescribed time by efficiently using an inexpensive electrolytic capacitor.

This circuit is provided with the aluminum electrolytic capacitor 2 for supplying a backup voltage VDD interposed between the power source input terminal 10 of a microcomputer IC1 operating at the time of inputting a chip enable voltage VCE higher than a threshold level from a chip enable terminal 11 and stopping operation at the time of inputting a voltage VCE lower than the threshold level and a power source 5, and an aluminum electrolytic capacitor 3 interposed between the power source 5 and the terminal 11. It is desirable to provide a voltage dropping circuit 4 for dropping the voltage VCE to be close to the threshold level between the capacitor 3 and the terminal 11.