1. A computer-implemented information searching method, comprising the steps of: extracting one or more non-content characteristics of a document from a document set; analyzing the extracted non-content characteristics; generating an optimizing tool based on analyzing results; and optimizing a preliminary search result with the generated optimizing tool, wherein the step of optimizing includes the steps of: selecting, from the preliminary search result, a resulting document sequence having relatively high reliability; calculating a distance from each of the documents in the preliminary search results to each document of the resulting document sequence; adjusting the reliability values of the documents in the resulting document sequence; and arranging the documents in descending order of the adjusted reliability values to obtain optimized results, and wherein the distance from each of the documents in the preliminary search results to the document of the resulting document sequence equals a sum of weights of sides passed through by a directional path between two documents, the distance is infinite when there is no path between the document in the preliminary search results and the document in the resulting document sequence, the distance from one document to itself is zero, the distance L between the document in the preliminary search results and the document in the resulting document sequence is expressed by the following equation when there are plural paths between the two documents, L=1/((1/L 1 )+(1/L 2 )+. .. +(1/LX)) where, L represents the distance between two documents, L 1 represents the distance of a path 1 , L 2 represents the distance of a path 2 , and LX represents the distance of a path X.