PURPOSE: To surely detect a fact that the contents stored in a memory are erased after the loss of a memory power supply and to hold the contents of the memory.

CONSTITUTION: When a normal power supply 2 is lost, the electric power is applied to a memory 8 from a battery 1 through a power switching circuit 6. Thus the storage contents of the memory 8 are hald. If the battery 1 is also lost, the cut-off of the power supply is detected owing to a fact that the T input of a flip-flop 11 is delayed by a delay circuit 1 even though one of the supply 2 and the battery 1 is recovered. Then the storage contents of the memory 8 are held until they are reset by a switch 13.