An arousal level determination device, which determines an arousal level of a driver driving a vehicle, includes a detection part and a determination part. The detection part is configured to detect an amount of body movement indicating a magnitude of movement of a body of the driver. The determination part is configured to determine the arousal level of the driver. The determination part determines that the driver is in an initial stage of decline in the arousal level when the amount of body movement has a decreasing trend.
