Abstract: An apparatus for chlorinating swimming bath water, includes an electrochemical cell (2) with an anolyte chamber (25) and a catholyte chamber (22), which are separated by an ion-selective diaphragm (290), a metering device (7) for supplying consumption hydrochloric acid to the cell (2), a chlorine gas outlet from the upper space (26) of the anolyte chamber (25), a chlorine gas pipe (29) for transferring chlorine gas from the cell (2), to a circulation pipe (15) for the bath water, an ejector (10) connecting the chlorine gas pipe (29) to the bath water pipe (15). The ejector (10) is adapted to generate a pressure in the chlorine gas pipe (29) which is lower than atmospheric pressure, and a gas flow in the gas pipe (29) which is greater than the greatest chlorine gas production flow of the cell (2). An atmospheric air pipe (35,45) communicates with the chlorine gas pipe (29). A liquid trap device (3) is arranged in the air pipe.