An overturn-notification-rider-informing-device (10, 10a, 10b) applied to a leaning-vehicle-overturn-notification-system (1, 1a, 1b), the leaning-vehicle-overturn-notification-system (1, 1a, 1b) being configured to notify overturn occurrence information indicating that a leaning vehicle changed from a travelling state to an overturned state to outside of the leaning vehicle by radio communication, the overturn-notification-rider-informing-device (10, 10a, 10b) being mounted in the leaning vehicle, the leaning vehicle comprising: a vehicle body configured to lean to the left when turning left and to lean to the right when turning right; and at least one of a front light configured to illuminate an area in front of the vehicle body when the vehicle body is in an upright state, indicators, a back light, a meter panel, an image display section, a horn or a buzzer; the overturn-notification-rider-informing-device (10, 10a, 10b) comprising: a leaning-vehicle-overturn-notification-information-acquisition-section configured to acquire notification preparation information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) is preparing to notify the overturn occurrence information to outside of the leaning vehicle by the radio communication, or notification completed information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) has notified the overturn occurrence information to outside of the leaning vehicle by the radio communication; and an overturn-notification-rider-informing-actuation-section that is configured to, based on the notification preparation information or the notification completed information acquired by the leaning-vehicle-overturn-notification-information-acquisition-section, cause light to be radiated or sound to be generated in a horizontal direction from the leaning vehicle that is in an overturned state by actuating at least one of the front light, the indicators, the back light, the meter panel, the image display section, the horn or the buzzer in an operating state that is different from an operating state at a time when, or immediately before, the leaning vehicle changes from a travelling state to an overturned state, and thereby is configured to inform a rider of an overturn notification state indicative of a status of notification of the overturn occurrence information. a vehicle body configured to lean to the left when turning left and to lean to the right when turning right; and at least one of a front light configured to illuminate an area in front of the vehicle body when the vehicle body is in an upright state, indicators, a back light, a meter panel, an image display section, a horn or a buzzer; the overturn-notification-rider-informing-device (10, 10a, 10b) comprising: a leaning-vehicle-overturn-notification-information-acquisition-section configured to acquire notification preparation information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) is preparing to notify the overturn occurrence information to outside of the leaning vehicle by the radio communication, or notification completed information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) has notified the overturn occurrence information to outside of the leaning vehicle by the radio communication; and an overturn-notification-rider-informing-actuation-section that is configured to, based on the notification preparation information or the notification completed information acquired by the leaning-vehicle-overturn-notification-information-acquisition-section, cause light to be radiated or sound to be generated in a horizontal direction from the leaning vehicle that is in an overturned state by actuating at least one of the front light, the indicators, the back light, the meter panel, the image display section, the horn or the buzzer in an operating state that is different from an operating state at a time when, or immediately before, the leaning vehicle changes from a travelling state to an overturned state, and thereby is configured to inform a rider of an overturn notification state indicative of a status of notification of the overturn occurrence information. a leaning-vehicle-overturn-notification-information-acquisition-section configured to acquire notification preparation information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) is preparing to notify the overturn occurrence information to outside of the leaning vehicle by the radio communication, or notification completed information indicating that the leaning-vehicle-overturn-notification-system (1, 1a, 1b) has notified the overturn occurrence information to outside of the leaning vehicle by the radio communication; and an overturn-notification-rider-informing-actuation-section that is configured to, based on the notification preparation information or the notification completed information acquired by the leaning-vehicle-overturn-notification-information-acquisition-section, cause light to be radiated or sound to be generated in a horizontal direction from the leaning vehicle that is in an overturned state by actuating at least one of the front light, the indicators, the back light, the meter panel, the image display section, the horn or the buzzer in an operating state that is different from an operating state at a time when, or immediately before, the leaning vehicle changes from a travelling state to an overturned state, and thereby is configured to inform a rider of an overturn notification state indicative of a status of notification of the overturn occurrence information.