An air-conditioning method suitable for reducing energy consumption is selected. A comparison unit 105 compares first operating efficiency, which is operating efficiency when only first air conditioning is performed, with second operating efficiency, which is operating efficiency when only second air conditioning is performed. The first air conditioning is air conditioning in an air-conditioning target space by an air conditioner, and the second air conditioning is air conditioning in the air-conditioning target space by supplying outdoor air without adjusting a temperature of the outdoor air to the air-conditioning target space. A decision unit 106 decides whether to perform the first air conditioning and whether to perform the second air conditioning, based on a result of comparison between the first operating efficiency and the second operating efficiency by the comparison unit 105.