4. A document analysis system, comprising an information processing apparatus including a processor, a storage unit, an input device, and an output device: wherein the storage unit stores two texts which are derived from documents and which are given from the input device; wherein the processor comprises: a common character string extractor configured to extract each of common character strings that is common between the two texts and that has a predetermined character string length, and to determine whether or not the two texts are to be set as Kolmogorov complexity calculation objects, based on both a number of the extracted common character strings and a predetermined number of common character strings, as a result of pretreatments of each similarity degree calculation of predetermine using the Kolmogorov complexity, wherein a pretreatment of the pretreatments refers to the number of extracted common character strings in an original language and determines whether a processing of the Kolmogorov complexity to the similarity degree calculation is to be performed, before performing a calculation processing of the Kolmogorov complexity between the two texts; a similarity degree calculation unit configured to calculate each similarity degree between the stored two texts in the storage unit, to calculate, when the two texts include the Kolmogorov complexity calculation objects determined by the common character string extractor, a similarity degree therebetween by using an approximation of a Kolmogorov complexity, and to handle, when the two texts are not the Kolmogorov complexity calculation objects, the similarity degree between the two texts as being dissimilar, and wherein each similarity degree of the stored two texts in the storage unit is supplied to at least one of the output device and the storage unit from the processor.
4. A document analysis system, comprising an information processing apparatus including a processor, a storage unit, an input device, and an output device: wherein the storage unit stores two texts which are derived from documents and which are given from the input device; wherein the processor comprises: a common character string extractor configured to extract each of common character strings that is common between the two texts and that has a predetermined character string length, and to determine whether or not the two texts are to be set as Kolmogorov complexity calculation objects, based on both a number of the extracted common character strings and a predetermined number of common character strings, as a result of pretreatments of each similarity degree calculation of predetermine using the Kolmogorov complexity, wherein a pretreatment of the pretreatments refers to the number of extracted common character strings in an original language and determines whether a processing of the Kolmogorov complexity to the similarity degree calculation is to be performed, before performing a calculation processing of the Kolmogorov complexity between the two texts; a similarity degree calculation unit configured to calculate each similarity degree between the stored two texts in the storage unit, to calculate, when the two texts include the Kolmogorov complexity calculation objects determined by the common character string extractor, a similarity degree therebetween by using an approximation of a Kolmogorov complexity, and to handle, when the two texts are not the Kolmogorov complexity calculation objects, the similarity degree between the two texts as being dissimilar, and wherein each similarity degree of the stored two texts in the storage unit is supplied to at least one of the output device and the storage unit from the processor. 15. The document analysis system according to claim 4 , wherein the document analysis system is configured to determine whether a similarity degree calculation of the Kolmogorov complexity is used by the processor.