1. A system for searching a plurality of texts for keywords determining an event occurrence in a plurality of texts wherein the texts each have a progress leading up to the event occurrence recorded therein, comprising: a text input unit for inputting a plurality of subtexts while associating each of the subtexts with an event occurring through the process recorded in each of the texts, the subtexts obtained by selecting parts corresponding to each of a plurality of predetermined sections in each of the plurality of texts; a plurality of event prediction devices corresponding to the plurality of sections respectively, the prediction devices each outputting a prediction result of an event occurring through the process recorded in the subtexts corresponding to the prediction device, the prediction result based on the appearance frequency of each word in the subtexts; a prediction device adjuster for adjusting the event prediction device corresponding to each of the plurality of sections, so as to maximize the percentage of agreeing texts to a first text group selected from the plurality of corresponding subtexts, the agreeing texts each indicating the content in which the inputted event agrees with the prediction result; a prediction processor for generating the prediction result for each of the plurality of sections, by selecting a second text group, which is different from the first text group, from the plurality of subtexts corresponding to the section, and then by inputting each text to the second text group in the adjusted event prediction device corresponding to the section; and a search unit for calculating the prediction precision for the second text group of the event prediction device of each of the sections, the prediction precision based on a comparison result between the inputted event and the prediction result for each subtext, for searching for keywords in a section which has a higher degree of prediction precision than a predetermined reference value, and for outputting the keywords.