A cooling device of a construction machine, comprising: at least one hydraulic motor (30a and 30b) that rotates positively and reversibly to correspond to a supplying direction of pressure oil and drives at least one rotatably cooling fan (20a and 20b) connected thereto, respectively; a switching valve switching rotation direction of the at least one hydraulic motor (30a and 30b) by switching the supplying direction of the pressure oil supplied to the at least one hydraulic motor (30a and 30b) from a hydraulic pump; and a first hydraulic line, which connects the switching valve with the hydraulic pump, characterized in that the cooling device comprises two or more hydraulic motors (30a and 30b) as the at least one hydraulic motor (30a and 30b), whose rotation directions are switched by the switching valve by switching the supplying direction of the pressure oil supplied to the two or more hydraulic motors (30a and 30b) from the hydraulic pump, wherein two or more flow rate makeup valves (50a and 50b) control an additional flow supplied upstream of the two or more hydraulic motors (30a and 30b) when a pressure drop is generated upstream of the two or more hydraulic motors (30a and 30b) on the basis of the supplying direction of the pressure oil, wherein the two or more flow rate makeup valves (50a and 50b) make up the flow to each pressure drop region of the two or more hydraulic motors (30a and 30b), and wherein the two or more flow rate makeup valves (50a and 50b) receive the flow from an oil tank and at least a first flow rate makeup valve of the two or more flow rate makeup valves (50a and 50b) is installed in a second hydraulic line connecting the first hydraulic line with the oil tank and at least a second flow rate makeup valve of the two or more flow rate makeup valves (50a and 50b) is installed in a third hydraulic line connecting the two or more hydraulic motors (30a and 30b) with the oil tank. at least one hydraulic motor (30a and 30b) that rotates positively and reversibly to correspond to a supplying direction of pressure oil and drives at least one rotatably cooling fan (20a and 20b) connected thereto, respectively; a switching valve switching rotation direction of the at least one hydraulic motor (30a and 30b) by switching the supplying direction of the pressure oil supplied to the at least one hydraulic motor (30a and 30b) from a hydraulic pump; and a first hydraulic line, which connects the switching valve with the hydraulic pump, characterized in that the cooling device comprises two or more hydraulic motors (30a and 30b) as the at least one hydraulic motor (30a and 30b), whose rotation directions are switched by the switching valve by switching the supplying direction of the pressure oil supplied to the two or more hydraulic motors (30a and 30b) from the hydraulic pump, wherein two or more flow rate makeup valves (50a and 50b) control an additional flow supplied upstream of the two or more hydraulic motors (30a and 30b) when a pressure drop is generated upstream of the two or more hydraulic motors (30a and 30b) on the basis of the supplying direction of the pressure oil, wherein the two or more flow rate makeup valves (50a and 50b) make up the flow to each pressure drop region of the two or more hydraulic motors (30a and 30b), and wherein the two or more flow rate makeup valves (50a and 50b) receive the flow from an oil tank and at least a first flow rate makeup valve of the two or more flow rate makeup valves (50a and 50b) is installed in a second hydraulic line connecting the first hydraulic line with the oil tank and at least a second flow rate makeup valve of the two or more flow rate makeup valves (50a and 50b) is installed in a third hydraulic line connecting the two or more hydraulic motors (30a and 30b) with the oil tank.