Abstract: When image data of a bar code displayed on a cellular phone and read by a vending machine or the like are sent to a server apparatus, the apparatus converts the code to a numerical value. The apparatus divides the code value by divisor A to obtain remainder a, and divides the code value by divisor B to obtain remainder b. The least common multiple for the numeric value A and the numeric value B is greater than the difference between the maximum and minimum values that the bar code value assumes. The apparatus refers pointers registered in a storage position corresponding to remainder a in the first table and pointers registered in a storage position corresponding to remainder b in the second table. The apparatus authenticates the user when the same user information in a user database can be accessed from both the first table and the second table.