1. An information retrieval system comprising: a memory means for storing a set of individual data in which a firing pattern indicating a characteristic of information to be retrieved is combined with a value indicating a degree of coincidence of said firing pattern with data inputted as retrieval key information; fetching means for fetching one or more individual pieces of data from said memory means; operation means, connected to said fetching means, for effecting a genetic operation with respect to said fetched individual piece of data; processing means, composed of a neural network including a synapse coupling matrix generated by taking a correlation from an aggregation of said firing patterns to be embedded in the form of memory, for extracting recall information by receiving said firing pattern as a result of being operated by said operating means, executing a state updating operation of performing a sum-of-product operation and a threshold value process of said firing pattern with said synapse coupling matrix and recursively executing said state updating operation till said firing pattern converges in a steady-state; and evaluation means for giving an evaluation by collating said recall information extracted by said processing means with the retrieval key information, replacing, if a value of said evaluation is higher than an evaluation value of said fetched individual data, said individual data within said memory means with said recall information and rejecting, if lower than said evaluation value, said recall information; wherein the genetic operation includes a crossover operation, mutational operation, a complementing operation and a reverse operation which are executed in parallel.