The present invention relates to an air purification device for vehicles and the purpose of the present invention is to provide a DOR (Direct Ozone Reduction) system which suppresses deterioration in purifying function of the ozone purifier. Ozone purification rate of activated carbon correlates with probability that gas is contacted with the radiator. Also, wind velocity of the gas passing through a radiator correlates with car speed. Therefore, the ozone purification rate of the activated carbon correlates with the car speed, The grill shutter 22 is controlled in fully open condition when the car speed is within an area faster than Speed A shown in FIG. 6. When the car speed is slower than Speed A, the grill shutter 22 is controlled in closed condition as shown in FIG. 2 (A).