A processing device includes a control unit configured to perform: identifying a user when the user enters a vehicle and performing a process of guaranteeing a boarded state of the user while the user is in the vehicle; receiving information on a predetermined procedure for performing an authentication process from the user; and transmitting user information which is required for performing the predetermined procedure as information on the user of whom the boarded state in the vehicle is guaranteed to an external device that is installed at a first place for the predetermined procedure in a state in which the boarded state of the user is guaranteed.