An arousal level assessment system for assessing arousal level of a driver of a vehicle, the arousal level assessment system comprising: at least one first sensor (111,112,113,114,115,116); at least one second sensor (111,112,113,114,115,116); and a processor configured to acquire driving mode information that indicates a driving mode of the vehicle, the driving mode being selectable by the vehicle and/or the driver from a first mode in which travel control of the vehicle is performed by the driver and a second mode in which at least a portion of the travel control of the vehicle is automatically performed, assess which of the first mode or the second mode is selected based on the driving mode information, execute following to in a case where the first mode is selected, acquiring driving information that indicates a driving operation by the driver and/or indicates a driving state of the vehicle via the at least one first sensor, acquiring physiological information of the driver via the at least one second sensor, and assessing the arousal level based on the driving information and the physiological information, and execute following and in a case where the second mode is selected, acquiring the physiological information via the at least one second sensor, and assessing the arousal level based on the physiological information without referring to the driving information. at least one first sensor (111,112,113,114,115,116); at least one second sensor (111,112,113,114,115,116); and a processor configured to acquire driving mode information that indicates a driving mode of the vehicle, the driving mode being selectable by the vehicle and/or the driver from a first mode in which travel control of the vehicle is performed by the driver and a second mode in which at least a portion of the travel control of the vehicle is automatically performed, assess which of the first mode or the second mode is selected based on the driving mode information, execute following to in a case where the first mode is selected, acquiring driving information that indicates a driving operation by the driver and/or indicates a driving state of the vehicle via the at least one first sensor, acquiring physiological information of the driver via the at least one second sensor, and assessing the arousal level based on the driving information and the physiological information, and execute following and in a case where the second mode is selected, acquiring the physiological information via the at least one second sensor, and assessing the arousal level based on the physiological information without referring to the driving information. acquire driving mode information that indicates a driving mode of the vehicle, the driving mode being selectable by the vehicle and/or the driver from a first mode in which travel control of the vehicle is performed by the driver and a second mode in which at least a portion of the travel control of the vehicle is automatically performed, assess which of the first mode or the second mode is selected based on the driving mode information, execute following to in a case where the first mode is selected, acquiring driving information that indicates a driving operation by the driver and/or indicates a driving state of the vehicle via the at least one first sensor, acquiring physiological information of the driver via the at least one second sensor, and assessing the arousal level based on the driving information and the physiological information, and acquiring driving information that indicates a driving operation by the driver and/or indicates a driving state of the vehicle via the at least one first sensor, acquiring physiological information of the driver via the at least one second sensor, and assessing the arousal level based on the driving information and the physiological information, and execute following and in a case where the second mode is selected, acquiring the physiological information via the at least one second sensor, and assessing the arousal level based on the physiological information without referring to the driving information. acquiring the physiological information via the at least one second sensor, and assessing the arousal level based on the physiological information without referring to the driving information.