Information processing system includes a first certification device which executes a first temporary certification, creates a first temporary certificate, transmits it to an external device, carries out a first formal certification and creates the first formal certificate, a second certification device which executes a second temporary certification based on the first temporary certification, creates a second temporary certificate, transmits it to the external device, carries out a second formal certification and creates the second formal certificate, and a processing device which verifies a validity of the first formal certificate corresponding to the first temporary certificate and a validity of the second formal certificate corresponding to the second temporary certificate from the user, in response to a information processing request from the user and determines to execute the information processing corresponding to the information processing request based on the verification result.