Abstract: A control circuit device of a reverse osmosis drinking water machine has a microcomputer unit controlling the working of various peripheral circuits and enabling the drinking water machine to determine the quality of the drinking water and to clean automatically the filtration elements of the basis of the determined quality of the drinking water. The device is further provided with an output unit capable of giving an advance warning to remind the user of the need of replacing the worn-out filtration elements. The output unit is also capable of terminating automatically the water-making process when the PPM value of the drinking water so made is not in conformity with the health standard.