PURPOSE: To provide a controller capable of preventing the destruction of stored contents caused by power reduction.

CONSTITUTION: This controller is provided with an arithmetic controller 6 in which information installed in the arithmetic controller 6 for a controlled object is stored, a controller 21 controlling the rewrite of the information stored by the arithmetic controller 6 or the addition of another information, and a power source circuit 56 provided with a power reduction state detecting means for detecting the output state of a battery 36; and the storing operation of the arithmetic controller 6 and the execution or the non-execution of a control means are controlled by the controller 21 based on the detected result by the power reduction state detecting means of the circuit 56.