A state estimation value indicating a battery state is successively calculated from time to time according to a battery model capable of dynamically estimating the internal state of the secondary battery by using an inspection value of a sensor group indicating the secondary battery behavior. By using the sate estimation value at each moment estimated by the battery model expression at each predetermined cycle, an I/O-enabled time is predicted when a predetermined power is continuously inputted (charged) or outputted (discharged) from the current moment. A load operation instruction of the secondary battery is set so as to avoid overcharge and over-discharge of the secondary battery according to the operation request to the load and by considering the predicted characteristics between input/output power and input/output-allowed time.