Abstract: A data search system 1 conducts a search through a plurality of pieces of search target data to which at least date and time information is attached as attached data. The data search system includes search means for searching the plurality of pieces of search target data for keyword-matching data including a search keyword, and extracting, as a linked search keyword, the date and time information on a time period that is included in the attached data attached to the keyword-matching data, linked search means for searching the plurality of pieces of search target data for whether there exists linked matching data to which attached data including a time period that is close to the time period of the linked search keyword is attached, and output means for outputting the keyword-matching data and the linked matching data.