TRAVEL CONTROL DEVICE, TRAVEL CONTROL METHOD, AND COMPUTER-READABLE STORAGE MEDIUM STORING PROGRAM

A travel control device for controlling travel of a vehicle, comprises a device that acquires external information of a vehicle; a travel control unit configured to control travel of the vehicle using an acquisition result by the device; a diagnosis start unit configured to start a diagnosis process of the device; and a restriction unit configured to restrict a function of travel control of the vehicle after the diagnosis process of the device is started by the diagnosis start unit according to a state of travel control of the vehicle before the diagnosis process of the device is started.