A master node includes a locality determining table that stores data structures of obtained items, types of conditions that the items should meet, and locality information; a plan generating unit that generates a search plan; a determining unit that obtains the locality information corresponding to the data structure of the item obtained as a sequence and the type of condition for the item and determines whether the item is stored in a distributed manner across different databases; an updating unit that removes a request of creating a logical sequence from the search plan and updates the search plan when the item is not stored in a distributed manner across the different databases; and an execution requestexecution requesting unit that notifies a slave node of a search plan execution request. The slave node includes an execution request receiving unit and an executing unit that executes the search plan.