1. A data retrieval system for retrieving a character pattern from an input character string, comprising: a processor; a retrieval request block including: a shift register, having N 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 first partial character string; and a state number register which stores, using the processor, a first state number, said retrieval request block outputting a first retrieval key including said first partial character string stored in said shift register and the first state number at a first cycle of said shift clock; and a state transition memory for receiving said first retrieval key at said first cycle to operate a first retrieval based on said first 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, wherein an input entry of the plurality of input entries has 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 N, wherein an output entry of the plurality of output entries has a combination of a next state number and a pattern number specifying said character pattern, said pattern number being retrieved as a result of a state transition of the first state number from said current state number to said next state number effected by characters in said matching character pattern, wherein said state transition memory outputs said next state number and said pattern number as a result said first retrieval, said state number register receiving and storing therein said next state number output from said state transition memory, wherein the state transition memory performs a plurality of parallel retrievals including a second retrieval which is performed based on a second retrieval key including a second partial character string stored in said shift register at a second cycle of said shift clock, wherein said second retrieval is performed before said state transition memory outputs the result of the first retrieval, wherein the first and the second retrievals are performed on the same input character string.