1. A symbol string search apparatus for making a decision of whether or not a symbol string to be searched for exists in a symbol string to be searched, which is composed of symbols represented by codes, in a leading collation processing of a search to be combined with a posterior collation processing of the search, the symbol string search apparatus being connected to a CPU through an address bus and a data bus and comprising: function definition means connected to said data bus, for receiving from said CPU a command defining a function to be performed by the symbol string search apparatus, said function definition means holding said command until it receives a next command from said CPU; data input/output means for receiving a symbol string to be searched through said data bus and for providing a search result output; search processing means for performing said leading collation processing based on a function defined by said function definition means by matching the symbol string to be searched for, which is already stored in said search processing means, with the symbol string to be searched which is input to said data input/output means, said leading collation processing being performed plural times for a plurality of symbol strings to be searched while said function definition means is holding said command; and condition holding means for holding data indicative of an internal condition corresponding to the result of the search, the data held in said condition holding means being accessible by said CPU.