Abstract: An Eco-Driving diagnostic system capable of quantitatively comprehending fuel consumption with respect to each event and environmental-load emissions owing to the fuel consumption, an Eco-Driving diagnostic method and a business system using the same. An in-vehicle device set to a vehicle acquires from a vehicle sensor information necessary to comprehend fuel consumption and driving statuses of the vehicle. The information is transmitted to a center via a radio communication network. On the basis of the acquired information, there are calculated fuel consumption owing to the vehicle's driving and environmental-load emissions owing to the fuel consumption. Further, on the basis of the calculated information, contents including results of the diagnosis and advices are created to promote Eco-Driving. The contents are provided to terminals such as PCs, mobile terminals such as mobile phones and the like, which has already been popularized.