1. A data retrieval system for retrieving a character pattern from an input character string, comprising: a retrieval request block including: a shift register, having a plurality (N) of register stages, for responding to a shift clock to consecutively latch characters of said input character string in respective said register stages to generate a partial character string; and a state number register for storing therein a state number, said retrieval request block outputting a retrieval key including said partial character string stored in said shift register and a state number stored in said state number register at each cycle of said shift clock; and a state transition memory for receiving said retrieval key at said each cycle to operate a retrieval based on said retrieval key, said state transition memory storing therein a state transition table having a plurality of input entries and a plurality of output entries each corresponding to one of said input entries, each of said input entries having a combination of a current state number and a matching character pattern including N characters obtained from said character pattern by dividing said character pattern if said character pattern includes characters in number larger than said N, each of said output entries having a combination of a next state number and a pattern number specifying said character pattern which is retrieved as a result of a state transition from said current state number to said next state number effected by any of characters in said matching character pattern, said state transition memory operating for a plurality of said retrieval in parallel retrieval processings, to thereby output said next state number and said pattern number as a result of each of said retrievals, said state number register receiving and storing therein said next state number output from said state transition memory.