There is a need for making a user fully conscious about environmentally friendly driving. In an ecological driving system, a CPU allows a display apparatus to distinctively display fuel consumption according to the following idling states. One idling state results from engine warm-up. Another is useless idling state. Still another idling state results when a vehicle waits for turning to the left at an intersection or stops at a roadside. Yet another idling state results when the vehicle waits for turning to the right at an intersection. Still yet another idling state results when the vehicle waits forward at an intersection or stops due to traffic congestion.