An eco-drive assist apparatus that displays a state of fuel economy in real time, the eco-drive assist apparatus comprising: eco judgment means (13; 113; 262) for judging whether a current driving state of a vehicle is an efficient fuel economy state or a non-efficient fuel economy state based on a boundary value that is calculated based on a state quantity representing a current driving state of the vehicle and which distinguishes whether a current driving state of the vehicle is an efficient fuel economy state or a non-efficient fuel economy state; first display means (50; 150; 250) for displaying a fuel economy state by displaying a figure corresponding to the boundary value and a figure corresponding to a current value representing a current driving state of the vehicle to the boundary value; and second display means (80; 180; 280) for displaying whether the current driving state of the vehicle judged by the eco judgment means is an efficient fuel economy state or a non-efficient fuel economy state by turning on/off a lamp; wherein the first display means (50; 150; 250) fixedly-displays a figure corresponding to a boundary value in a predetermined place in a display area, and changes a display form of a figure corresponding to the current value according to a relative relation of the current value to the boundary value; and wherein the eco judgment means (13; 113; 262) use different values to the boundary value for the judgment between a case that a driving state moves from the efficient fuel economy state to the non-efficient fuel economy state and a case that a driving state moves from the non-efficient fuel economy state to the efficient fuel-economy state when judging the driving state of the vehicle displayed by the second display means (80; 180; 280), and the first display means (50; 150; 250) fixedly displays the boundary value at the same location both when the driving state judged by the eco judgment means is the efficient fuel economy state and when the driving state judged by the eco judgment means is the non-efficient fuel economy state. eco judgment means (13; 113; 262) for judging whether a current driving state of a vehicle is an efficient fuel economy state or a non-efficient fuel economy state based on a boundary value that is calculated based on a state quantity representing a current driving state of the vehicle and which distinguishes whether a current driving state of the vehicle is an efficient fuel economy state or a non-efficient fuel economy state; first display means (50; 150; 250) for displaying a fuel economy state by displaying a figure corresponding to the boundary value and a figure corresponding to a current value representing a current driving state of the vehicle to the boundary value; and second display means (80; 180; 280) for displaying whether the current driving state of the vehicle judged by the eco judgment means is an efficient fuel economy state or a non-efficient fuel economy state by turning on/off a lamp; wherein the first display means (50; 150; 250) fixedly-displays a figure corresponding to a boundary value in a predetermined place in a display area, and changes a display form of a figure corresponding to the current value according to a relative relation of the current value to the boundary value; and wherein the eco judgment means (13; 113; 262) use different values to the boundary value for the judgment between a case that a driving state moves from the efficient fuel economy state to the non-efficient fuel economy state and a case that a driving state moves from the non-efficient fuel economy state to the efficient fuel-economy state when judging the driving state of the vehicle displayed by the second display means (80; 180; 280), and the first display means (50; 150; 250) fixedly displays the boundary value at the same location both when the driving state judged by the eco judgment means is the efficient fuel economy state and when the driving state judged by the eco judgment means is the non-efficient fuel economy state.