1. A similarity detecting system, comprising: a processor; and a memory coupled to the processor, wherein the memory stores instructions that cause the processor to: retain a table related to random number data generated based on a parameter for setting a similarity criterion; register and manage the search object data on the table; carry out a similarity detection by using the table based on the similarity criterion in response to a nearest neighbor search request from an optional reference point, and output data detected to be a nearest neighborhood; set a plurality of said different similarity criteria; retain a plurality of said tables which are respectively related to said plurality of different similarity criteria; and manage the search object data by the plurality of tables in parallel.