Abstract: A liquid quality-evaluating apparatus for liquids whose boiling point or vapor lock point vary by deterioration includes a heating vessel made of heat conductive and electrically conductive material and adapted to hold a brake fluid whose quality is to be determined. The heating vessel has an opening which is closed by an electrically and heat insulating removable cover and the wall of the heating vessel near the bottom is fitted with a nozzle acting as a siphon. The cover carries a hollow cylindrical electrode so disposed as to slightly dip into a brake fluid received in the vessel. A heat-responsive resistance element for detecting the temperature of the brake fluid is received in the hollow cylindrical electrode. A heater is provided below the heating vessel to heat the brake fluid received therein. A current cutoff-detecting circuit is electrically connected between the heating vessel and the hollow cylindrical electrode.