Upon implementing a data registration into or a data retrieval from a data table (3) where first item data are registered along with corresponding second item data, there are used a first pointer table (1) where pointers to part of the registered data in the data table are registered in storage positions that are designated by hash values obtained by applying a first hash function (6) to the first item data of the part of the registered data, and a second pointer table (2) where pointers to the other registered data in the data table are registered in storage positions that are designated by hash values obtained by applying a second hash function (22) to the first item data of the other registered data.