A ticket issuing device issues a highly convenient electronic ticket. The electronic ticket is formed of validity data and information to be validated. The validity data includes a secret key to which an algorithm whose presence is verifiable without being exposed is applicable. The information to be validated includes a public key corresponding to the secret key for verifying the presence of the secret key. The information is validated by the validity data. A ticket storage device generates a digital signature for verifying the presence of the secret key in the validity data, and sends the digital signature together with the information to be validated to a ticket checking device. The ticket checking device determines the presence of the secret key in the ticket storage device by using the digital signature from the ticket storage device and the public key contained in the information to be validated.