A fuel-saving control device, comprising: a surplus driving force calculation unit for calculating a surplus driving force based on a difference between a driving force of a driving wheel on a vehicle that corresponds to an instructed fuel injection amount depending on an accelerator position and a travelling resistance force on the vehicle; and a fuel-saving control unit configured to execute a fuel-saving control for lowering and correcting an instructed fuel injection amount depending on an accelerator position by using a lowering correction value depending on the surplus driving force when the surplus driving force becomes equal to or greater than a first threshold value, and configured to stop the fuel-saving control when the surplus driving force becomes smaller than the first threshold value, further comprising: a vehicle position detection unit for detecting a vehicle position; a map information storage unit for storing map information; and a front curvature radius identification unit for identifying a front curvature radius based on the vehicle position and the map information, wherein, when the front curvature radius is smaller than a second threshold value during execution of the fuel-saving control, the fuel-saving control unit is configured not to change the lowering correction value at a change rate that is equal to or greater than a predetermined change rate. a surplus driving force calculation unit for calculating a surplus driving force based on a difference between a driving force of a driving wheel on a vehicle that corresponds to an instructed fuel injection amount depending on an accelerator position and a travelling resistance force on the vehicle; and a fuel-saving control unit configured to execute a fuel-saving control for lowering and correcting an instructed fuel injection amount depending on an accelerator position by using a lowering correction value depending on the surplus driving force when the surplus driving force becomes equal to or greater than a first threshold value, and configured to stop the fuel-saving control when the surplus driving force becomes smaller than the first threshold value, further comprising: a vehicle position detection unit for detecting a vehicle position; a map information storage unit for storing map information; and a front curvature radius identification unit for identifying a front curvature radius based on the vehicle position and the map information, wherein, when the front curvature radius is smaller than a second threshold value during execution of the fuel-saving control, the fuel-saving control unit is configured not to change the lowering correction value at a change rate that is equal to or greater than a predetermined change rate. a vehicle position detection unit for detecting a vehicle position; a map information storage unit for storing map information; and a front curvature radius identification unit for identifying a front curvature radius based on the vehicle position and the map information, wherein, when the front curvature radius is smaller than a second threshold value during execution of the fuel-saving control, the fuel-saving control unit is configured not to change the lowering correction value at a change rate that is equal to or greater than a predetermined change rate.