To reduce operating costs of a water heater.

An optimum operating rule creating section 111 creates an operating rule by using GA (Genetic Algorithm) while performing simulation of the water heater by a simulating section 112. The simulating section 112 performs the simulation of the water heater by using calendar information stored by a calendar information storing section 102, an operating information stored by an operating information storing section 104, an environmental information stored by an environmental information storing section 106, and electricity charges stored by an electricity charge storing section 108. An environmental change detecting section 110 detects the change of operating environment of the water heater, and the optimum operating rule creating section 111 creates the operating rule when the operating environment changes.