To efficiently retrieve information related to things to happen in the future with high accuracy, when retrieving objective information from among information on the Internet using keywords.
When receiving a retrieval request including a keyword from a terminal 2, a retrieval server 3 retrieves information on the Internet on the basis of the keyword (step S2). Pieces of information including pre-set "expression indicating future time" are extracted from the retrieval result (step S3), and time of generation for each piece of the extracted information is determined (step S4). Pieces of information whose "future time" in each piece of information is after the day of retrieval are left and other pieces of information are excluded from the retrieval result, on the basis of the obtained time of generation (step S5). If there is content which can be estimated as a day of generation in a document of each piece of information, time of information generation is determined on the basis of the content, but if the content does not exist, time of generation is determined on the basis of a timestamp which is certainly added to each piece of information.
Osamu Suzawa
Kazuhiko Miyasaka