An electric power acquisition section acquires a power demand of a load. An assist control section determines that an assist condition is satisfied when the power demand exceeds a threshold value within a time slot for permitting electric power to be supplied to the load. When determining that the assist condition is satisfied, the assist control section presents a selection prompt to inquire whether or not to activate an assist operation for supplying the electric power from a power storage device, on an operation display device through a notification control section. If there is a response for requesting activation of the assist operation from the operation display device in response to the selection prompt, the assist operation is started. The assist condition is set in a storage unit by a condition setting section.