An authentication method for authenticating an electronic ticket stored in a portable information device by an authentication apparatus, including a step of acquiring, by the portable information device, shared information that is sharable with the authentication apparatus when authentication of the electronic ticket is performed, a step of generating, by the portable information device, a bar code based on the acquired shared information and the electronic ticket, a step of displaying the bar code by the portable information device, a step of reading, by the authentication apparatus, the electronic ticket and the shared information from the bar code displayed on the portable information device, and a step of performing, by the authentication apparatus, the authentication of the electronic ticket by making a comparison between contents of the shared information read from the bar code together with the electronic ticket and shared information in the authentication apparatus.