1. A method of generating time-series data from Web pages, comprising: collecting Web pages, which match a user's designated collection condition, from a plurality of Web sites, the collecting including storing the collected Web pages in a storage device; dividing a set of Web pages stored in the storage device into a plurality of clusters, based on URL information of the Web pages; extracting a date expression from Web pages included in each of the clusters; determining a typical date expression form for each of the clusters, based on the extracted date expression; dividing the Web pages included in each of the clusters into a plurality of items with reference to a location where a date expression of the date expression form appears, based on the date expression form; and generating time-series data for each of the clusters by sorting the items for each of the clusters in order of time, based on date expressions corresponding to the items.