To provide a personal information safety operating method with which the secrecy of personal information is kept even when performing communication while using a public network in an internet system.

A questionaire answer and a personal ID are communicated on a public network 4 between a user terminal 1 and a world wide web(WWW) server 3, the personal ID and the correspondent personal information are transmitted as data enciphered by a cryptographic key in a disclosed key enciphering system on the public network 4 between a provider terminal 2 and the WWW server 3, and the enciphered data are deciphered while using a deciphering key paired with the cryptographic key on the side of reception.