Provided is a server that communicates, via a network, with at least one air conditioner that executes a normal operation or a loosening operation includes a determination unit that determines a heat exposure period for each air conditioning target space, the indoor solar irradiance information indicating a transition of solar irradiance, and the heat exposure period being a time duration in which an environment in the air conditioning target space is likely to be influenced by solar radiation, a generation unit that generates operation plan information of designating a loosening operation period, the loosening operation period being a time duration in which the air conditioner is caused to execute the loosening operation, and a supply unit that supplies the operation plan information to the air conditioner via the network to cause the air conditioner to execute the loosening operation in the loosening operation period.