An autonomous driving assistance device includes a manual driving control section, an autonomous driving control section, and a travelling condition determining section. If it is detected that there is a malfunction in a first sensor during control of the autonomous driving of the vehicle, the autonomous driving control section executes emergency autonomous driving until a predetermined condition is satisfied while changing, based on the determined travelling condition, a driving manner of an emergency autonomous driving as compared with a driving manner of the autonomous driving executed before no malfunctions are detected in the first sensor; and after the emergency autonomous driving is terminated, the autonomous driving assistance device being configured to selectively execute one of: causing the autonomous driving control section to stop the vehicle; and causing the manual driving control section to control the manual driving.