1. A document information search system for searching document information, the system comprising: a plurality of document information search apparatuses connected to a communication network, each of the document information search apparatuses operating in parallel to each other in accordance with search conditions broadcast from a plurality of search terminals connected to said communication network, said plurality of search terminals receiving and displaying search results transmitted from said plurality of document information search apparatuses, each of the plurality of document information search apparatuses including: a text data storage means for storing a document text data group; a search expression input means for inputting a search conditional expression in which a complex condition is designated including key words for searching said document text data group, and positional and logical relationships among said key words; a search expression analysis means for analyzing the inputted search conditional expression to extract a search subject key word and a complex condition descriptive portion; a synonym development means for generating synonyms of said search subject key word based on said search subject key word outputted from said search expression analysis means; a different notation development means for generating different notation words of said search subject key word, and said synonyms; a complex condition analysis means for analyzing said complex condition descriptive portion outputted from said search expression analysis means and developing said complex condition descriptive portion into said positional and logical relationships; at least one term comparator means for reading text data from said text data storage means and collectively comparing said text data with respect to said different notation words generated by said different notation development means; at least one complex condition judgment means for detecting documents corresponding to conditions designated by said complex condition analysis means based on results of a comparison outputted from said at least one term comparator means and outputting identifiers of the detected documents; a search result output means for outputting identifier information of the documents corresponding to said search conditional expression based on the identifiers outputted from said at least one complex condition judgment means; and, a communication means connected to said communication network for receiving said search conditional expression and supplying the search conditional expression to said search expression input means and for forwarding the identifier information from said search result output means to an operatively associated search conversation terminal from which a search request corresponding to the identifier information is transmitted.