A personal identity authenticating system where the registrant/cardholder and the registrar are assigned specific identifiers and secret keys and public keys that are mapped to the identifiers at the authentication support station (ASS). Personal identity to which the registrar identifier is attached is encrypted wit the registrant/cardholder's secret key. Personal identity data is embedded as an encrypted watermark image data by means of the registrar's secret key. Both encrypted identity and watermarked image data are recorded on the IC card. When authentication is required, the identity data with the registrar identifier is decrypted with the cardholder's public key that is supplied by the ASS. The registrar's public key is obtained from the ASS by using the decrypted registrar identifier. The registrar's public key permits the personal identity to be retrieved from the watermarked image data. Internal authentication is executed by matching between personal identity strings and image data.