Update device, indoor and outdoor unit, update system, update method, and program

The update device is a device connected to a communication line connecting a plurality of indoor and outdoor units, and is provided with: an error notification invalidation instruction unit that instructs the plurality of indoor and outdoor units to not perform an error notification even if a return is not received from the indoor and outdoor unit to be updated; an update processing unit that performs program update processing on the indoor/outdoor unit to be updated; and an error notification validity instruction unit that instructs the plurality of indoor and outdoor units to perform an error notification when no reply is received from the indoor and outdoor unit to be updated. 更新装置为与连接多个室内外机的通信线路连接的装置，其具备：错误通知无效化指示部，对多个室内外机指示即使在从更新对象的室内外机未接收到回信的情况下也不进行错误通知；更新处理部，对更新对象的室内外机进行程序的更新处理；及错误通知有效化指示部，对多个室内外机指示在从更新对象的室内外机未接收到回信时进行错误通知。