Stream data is provided for realizing precise calculation processing to keep a constant memory usage of a query including a time-based window, and to take all of input data into consideration. A stream data processing server sections the time-based window into sub-windows each with a smaller width by a query time resolution change unit, and a query processing engine executes the aggregation processing based on the sub-window when receiving the stream data to generate an aggregation tuple, and calculates the calculation result of the query including the time-based window by aggregation processing on the aggregation tuple.