PURPOSE: To permit to open and close the hinged louver plates of radiator shutter automatically with a simple structure by a method wherein the displacement of a piston, displaced by receiving the pressure of cooling water, is transmitted to the open-close plates.

CONSTITUTION: When the level of cooling water for an engine is elevated, a pressure in a tank space Q is increased, and when a force, received by a pressure receiving plate 11a, has exceeded the energizing force of a spring 10, the piston 11 moves to the left. When the piston 11 moves to the left, a connecting member 12 is pivoted clockwise about a point 12a. A slide member 14 moves to the direction of an arrow sign B in accordance with the pivoting of the connecting member 12. In this case, a connecting point 24a moves to the arrow sign direction B together with the slide member 14, however, a fixed point 24b stays at present location, therefore, the positions of the hinged louver plates 1a are changed from series relation into parallel relation to pass cooling air through the radiator 2. Heat exchange is effected between the cooling air and the high- temperature cooling water, flowing through a tube 21, and the temperature of the cooling water is reduced thereby effecting good engine cooling.