A document search apparatus which causes a plurality of document management systems (105, 130, 140, 150) to execute a document search in parallel, and which comprises: a sending unit which is adapted to send a first query to each of said plurality of document management systems, the first query regarding a first search condition which is input, and a receiving unit which is adapted to receive a result of the search for the first query from each of said plurality of document management systems, and the apparatus being characterized by: a search control unit which causes said sending unit to send a second query comprising a search refinement condition which is input for requesting search refinement for the first query to at least one of the document management systems before receiving the result of the search from all of the document management systems and after receiving the result of the search from at least one of the document management systems, wherein the search refinement condition is automatically set when a number of hits in the results of the search received by the receiving unit is equal to or greater than a pre-determined number, based on information for limiting the search set in advance, wherein said search control unit comprises a management unit which manages a response state of each of said document management systems; and a selection unit which selects a scheme for requesting the second query of at least one of the document management systems according to the response state managed by said management unit, wherein said search control unit causes said sending unit to send the second query to at least one of the document management systems by using the scheme selected by said selection unit, wherein the second query causes said at least one of the document management systems to execute a search refinement with the search refinement condition according to the selected scheme, and wherein the receiving unit is further adapted to receive a result of the search for the second query from said at least one of the second document management systems. a sending unit which is adapted to send a first query to each of said plurality of document management systems, the first query regarding a first search condition which is input, and a receiving unit which is adapted to receive a result of the search for the first query from each of said plurality of document management systems, and the apparatus being characterized by: a search control unit which causes said sending unit to send a second query comprising a search refinement condition which is input for requesting search refinement for the first query to at least one of the document management systems before receiving the result of the search from all of the document management systems and after receiving the result of the search from at least one of the document management systems, wherein the search refinement condition is automatically set when a number of hits in the results of the search received by the receiving unit is equal to or greater than a pre-determined number, based on information for limiting the search set in advance, wherein said search control unit comprises a management unit which manages a response state of each of said document management systems; and a selection unit which selects a scheme for requesting the second query of at least one of the document management systems according to the response state managed by said management unit, wherein said search control unit causes said sending unit to send the second query to at least one of the document management systems by using the scheme selected by said selection unit, wherein the second query causes said at least one of the document management systems to execute a search refinement with the search refinement condition according to the selected scheme, and wherein the receiving unit is further adapted to receive a result of the search for the second query from said at least one of the second document management systems. a search control unit which causes said sending unit to send a second query comprising a search refinement condition which is input for requesting search refinement for the first query to at least one of the document management systems before receiving the result of the search from all of the document management systems and after receiving the result of the search from at least one of the document management systems, wherein the search refinement condition is automatically set when a number of hits in the results of the search received by the receiving unit is equal to or greater than a pre-determined number, based on information for limiting the search set in advance, wherein said search control unit comprises a management unit which manages a response state of each of said document management systems; and a selection unit which selects a scheme for requesting the second query of at least one of the document management systems according to the response state managed by said management unit, wherein said search control unit causes said sending unit to send the second query to at least one of the document management systems by using the scheme selected by said selection unit, wherein the second query causes said at least one of the document management systems to execute a search refinement with the search refinement condition according to the selected scheme, and wherein the receiving unit is further adapted to receive a result of the search for the second query from said at least one of the second document management systems.