An air-conditioning system control device configured to control one or a plurality of air-conditioning apparatus installed in a building, comprising: - an air-conditioning apparatus data obtaining unit configured to obtain operation data of the one or plurality of air-conditioning apparatus; - a heat load estimation obtaining unit configured to obtain a heat load estimation for the building; and - an air-conditioning apparatus control command determining unit configured to determine an air-conditioning apparatus control command so that a preset evaluation index satisfies a preset condition in a preset control-target period under a preset constraint, the air-conditioning apparatus control command determining unit configured to include time sections set therein, to divide the control-target period into a plurality of time periods by one or a plurality of preset division intervals, configured to determine a room-temperature change permissible range, a room temperature included in the operation data satisfying the constraint within the room-temperature change permissible range, configured to determine a heat-load change permissible range, based on the room temperature included in the operation data, the room-temperature change permissible range, the heat load estimation, and a heat load to be processed by the one air-conditioning apparatus or a heat load to be processed by each of the plurality of air-conditioning apparatus, and configured to determine, for each of the plurality of time sections, as the air-conditioning apparatus control command, an operation frequency and start-stop of the one or plurality of air-conditioning apparatus, based on the heat-load change permissible range and an operation efficiency of the one air-conditioning apparatus or an operation efficiency of each of the plurality of air-conditioning apparatus, characterized by the air-conditioning apparatus control command determining unit including a heat-load change permissible range estimating unit configured to determine the heat-load change permissible range, based on a measured room temperature, a preset upper-limit room-temperature set value serving as the constraint, a preset lower-limit room-temperature set value serving as the constraint, a building component physical property value indicating a heat-insulating property of the building and a heat-storage property of the building, and the heat load estimation. - an air-conditioning apparatus data obtaining unit configured to obtain operation data of the one or plurality of air-conditioning apparatus; - a heat load estimation obtaining unit configured to obtain a heat load estimation for the building; and - an air-conditioning apparatus control command determining unit configured to determine an air-conditioning apparatus control command so that a preset evaluation index satisfies a preset condition in a preset control-target period under a preset constraint, the air-conditioning apparatus control command determining unit configured to include time sections set therein, to divide the control-target period into a plurality of time periods by one or a plurality of preset division intervals, configured to determine a room-temperature change permissible range, a room temperature included in the operation data satisfying the constraint within the room-temperature change permissible range, configured to determine a heat-load change permissible range, based on the room temperature included in the operation data, the room-temperature change permissible range, the heat load estimation, and a heat load to be processed by the one air-conditioning apparatus or a heat load to be processed by each of the plurality of air-conditioning apparatus, and configured to determine, for each of the plurality of time sections, as the air-conditioning apparatus control command, an operation frequency and start-stop of the one or plurality of air-conditioning apparatus, based on the heat-load change permissible range and an operation efficiency of the one air-conditioning apparatus or an operation efficiency of each of the plurality of air-conditioning apparatus, configured to include time sections set therein, to divide the control-target period into a plurality of time periods by one or a plurality of preset division intervals, configured to determine a room-temperature change permissible range, a room temperature included in the operation data satisfying the constraint within the room-temperature change permissible range, configured to determine a heat-load change permissible range, based on the room temperature included in the operation data, the room-temperature change permissible range, the heat load estimation, and a heat load to be processed by the one air-conditioning apparatus or a heat load to be processed by each of the plurality of air-conditioning apparatus, and configured to determine, for each of the plurality of time sections, as the air-conditioning apparatus control command, an operation frequency and start-stop of the one or plurality of air-conditioning apparatus, based on the heat-load change permissible range and an operation efficiency of the one air-conditioning apparatus or an operation efficiency of each of the plurality of air-conditioning apparatus,