1. A mismatch detection system, comprising an input portion comprising a device configured to receive an input from a user, the input being a document which is written in a natural language; a computing portion, comprising a computer processor, configured to process the document; and an output portion configured to output the processed information, and connected to the computing portion, wherein the computing portion comprises: a statement unit extracting portion that extracts a set of statement units by dividing the given document into pieces; a statement constructing portion that constructs each statement as a combination of a context and specifics by sorting each of the statement units into the context, which indicate additional information of statements, and the specifics, which indicate information of the statements; a data generating portion that generates a data set obtained by merging a set of predetermined check specifics and a set of the statements generated by the statement constructing portion; a clustering portion that converts two most similar pieces of data in the generated data set into one new piece of data which is generated by linking the two most similar pieces of data, repeats the conversion to generate a new data set, and extracts, from the generated new data set, only pieces of data that contain the statements generated by the statement constructing portion, to thereby generate a clustering result set; and a detection portion that generates a check item for each combination of a predetermined check subject and check specifics, and detects a mismatch of the statements based on a degree of similarity between the generated check item and a clustering result, the mismatch constituting a detection result; wherein the output portion outputs the detection result of the detection portion; wherein the statement constructing portion: sorts each statement unit as the specifics when the statement unit contains a verb, and as the context when the statement unit does not contain a verb, and generates the statement by linking the specifics and an immediately preceding context with a predetermined segmentation symbol which separates the specifics from the immediately preceding context; and wherein the detection portion generates the check item by linking the predetermined check subject and the check specifics with a predetermined segmentation symbol which separates the predetermined check subject from the check specifics.