Abstract: An auger-type ice making machine has a refrigerating cylinder having upper and lower bearings, an auger supported rotatably within the refrigerating cylinder by the upper and lower bearings, a water supply valve for supplying water to the refrigerating cylinder, a drain valve in fluid communication with the refrigerating cylinder for discharging water therefrom, an electric detector assembly including an electrode member having its one end extending into the refrigerating cylinder, and an electric control circuit electrically connected to the electrode member to receive a detection signal from the electric detector assembly. The electric control circuit determines on the basis of the detection signal that the impurity concentration of the water has increased beyond a predetermined level.