A fuel-saving control device equipped with: a surplus drive force calculation unit for calculating surplus drive force; a fuel-saving control unit for executing a fuel-saving control which lowers and corrects the indicated fuel injection amount according to the accelerator position when the surplus drive force reaches or exceeds a first threshold, and stopping the fuel-saving control when the surplus drive force falls below the first threshold; a vehicle position detection unit for detecting the vehicle position; a map information storage unit for storing map information; a road information identification unit for identifying the curvature radius and gradient of the road upon which travel is planned, on the basis of the vehicle position and the map information; and a flat/straight road determination unit for determining whether or not the road upon which travel is planned is a flat and straight road, on the basis of the curvature radius and gradient of the road upon which travel is planned. Therein, the fuel-saving control unit executes the fuel-saving control when the road upon which travel is planned is a flat and straight road.