A fuel-saving control device 100 equipped with: a surplus drive force calculation unit 101 for calculating surplus drive force; a fuel-saving control unit 102 for executing a fuel-saving control which lowers and corrects the indicated fuel injection amount according to the accelerator position by using a lowering-correction value that corresponds to the surplus drive force when the surplus drive force reaches or exceeds a prescribed threshold, and stopping the fuel-saving control when the surplus drive force falls below the prescribed threshold; a vehicle position detection unit 107 for detecting the vehicle position; a map information storage unit 108 for storing map information; and a forward curvature radius identification unit 109 for identifying the forward curvature radius on the basis of the vehicle position and the map information. Therein, the fuel-saving control unit 102 prevents the lowering-correction value from varying by a prescribed degree of variability or more when the forward curvature radius is less than the prescribed threshold.