PURPOSE: To provide a device capable of softening water (pure water formation) and deaeration through one system, reduce its istallig space and cost and futher reduce a troublesome monitoring on treating water.

CONSTITUTION: A water heating module 1 is provided with a water vapor permeable film 2 so as to divide an inside part of a water treating module 1 into a raw water chamber 11 and a permeable chamber 12. A raw water supplying line 3 is connected to the raw water chamber 11, a discharging line 6 having a permeated water tank 4 and a vacuum pump 5 inserted therein is connected to the permeable chamber 12, and then the permeated water tank 4 and a boiler 7 are connected by a water supplying line 9 having a water supplying pump 8 inserted therein.