2. A non-transitory computer-readable recording medium having recorded thereon a document analysis program for causing a computer including a processor, a storage unit, an input device, and an output device, the processor operates by the document analysis program as: to receive a plurality of texts from the storage unit; to extract each common character string having a predetermined character string length from the plurality of texts in the storage unit; to determine whether or not a a two texts of the plurality of texts are to be set as Kolmogorov complexity calculation objects, based on a number of the extracted each common character strings and a predetermined number of common character strings, as a result of pretreatments of each similarity degree calculation of the plurality of texts by 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; to calculate each similarity degree of the plurality of texts, when the two texts are the Kolmogorov complexity calculation objects, calculating the similarity degree of a Kolmogorov complexity, and when the two texts are not the Kolmogorov complexity calculation objects, handling the similarity degree between the stored two texts in the storage unit as being dissimilar; and to output the each similarity degree of the plurality of texts to at least one of the output device and the storage unit.
2. A non-transitory computer-readable recording medium having recorded thereon a document analysis program for causing a computer including a processor, a storage unit, an input device, and an output device, the processor operates by the document analysis program as: to receive a plurality of texts from the storage unit; to extract each common character string having a predetermined character string length from the plurality of texts in the storage unit; to determine whether or not a a two texts of the plurality of texts are to be set as Kolmogorov complexity calculation objects, based on a number of the extracted each common character strings and a predetermined number of common character strings, as a result of pretreatments of each similarity degree calculation of the plurality of texts by 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; to calculate each similarity degree of the plurality of texts, when the two texts are the Kolmogorov complexity calculation objects, calculating the similarity degree of a Kolmogorov complexity, and when the two texts are not the Kolmogorov complexity calculation objects, handling the similarity degree between the stored two texts in the storage unit as being dissimilar; and to output the each similarity degree of the plurality of texts to at least one of the output device and the storage unit. 3. The non-transitory computer-readable recording medium according to claim 2 , wherein the processor operates by the document analysis program as to output said each similarity degree of the plurality of texts to the output device and the storage unit.