A seat adjustment device includes: an authentication unit that is configured to identify plural occupants of a vehicle; an acquisition unit that is configured to acquire information relating to each one of the plural vehicle occupants identified by the authentication unit; a determination unit that is configured to determine relationships between the plural vehicle occupants based on information acquired by the acquisition unit; and a control unit that is configured to control at least one of a position or an orientation of seats mounted in the vehicle based on determination results from the determination unit.