A computer for a service provider receives from each member of two groups who is a user of a service via a mediating computer, a priority list in which member IDs of the other group is permuted in the priority order of a user and processing information that are encrypted so as not to be decrypted by the mediating computer. The ID of the priority list is encrypted with an encrypting key that is common to all members. The computer for a service provider performs matching, with ID in the priority list being left encrypted when the list is decrypted. The computer for a service provider decrypts the processing information, makes it in a state in which the matching result can be decrypted based on the processing information by only a person concerned, and sends it to each member via the mediating computer.