A cooling device of a construction machine according to the present invention includes: two or more hydraulic motors that rotate positively and reversibly to correspond to a supplying direction of pressure oil and drives rotatably cooling fans connected thereto, respectively; a switching valve switching rotation directions of the two or more hydraulic motors by switching the supplying direction of the pressure oil supplied to the two or more hydraulic motors from the hydraulic motor; and flow rate makeup valves controlling an additional flow supplied upstream of the two or more hydraulic motors when a pressure drop is generated upstream of the two or more hydraulic motors on the basis of the supplying direction of the pressure oil.