Electronic Control Device, Control Method, and Automated Driving System

An electronic control device that is mounted on a vehicle and performs automated driving control using map information includes: a storage unit that stores basic map data; a communication unit that communicates with a data center to acquire map data managed by the data center as external map data; and a processing unit that determines a control mode of the automated driving control according to the acquired external map data and performs the automated driving control based on the determined control mode, position information of the vehicle, the basic map data, and the external map data. With the configuration, availability of map information is secured and continuity of an automated driving function is improved even in a case where a communication situation is not good while a required storage capacity is suppressed by limiting the map information stored in the vehicle.