4. The search device according to claim 3 , wherein the memory device further comprises a memory area which stores an index showing the position where each of the N-gram strings contained in multiple search target character strings and containing a prescribed number of characters appears in the search target character string; wherein the designator designates the position where the N-gram strings appear using the index.
4. The search device according to claim 3 , wherein the memory device further comprises a memory area which stores an index showing the position where each of the N-gram strings contained in multiple search target character strings and containing a prescribed number of characters appears in the search target character string; wherein the designator designates the position where the N-gram strings appear using the index. 5. The search device according to claim 4 , wherein: the index, after the multiple search target character strings are grouped based on character length, contains information compiling references to the search target character string for each group; and the designator executes the designation process for the search target character strings contained in groups in which the difference between the character length of the group and the character length of the search character string is smaller than a prescribed threshold value, and omits the designation process for search target character strings contained in groups in which the difference is larger than the prescribed threshold value.