A database management system has a query interface for receiving a query and a query executor for executing the received query. The query executor dynamically generates a task, and executes a plurality of tasks in parallel. In execution of each task, each time data is required to be read from a database, the query executor generates a task for acquiring the data, and in execution of the generated task, issues a data read request for reading the data from the database, to thereby shorten a time taken to execute each task.