To reduce pressure loss at the time of flowing water in a water softening apparatus having constitution of serial installation of two or more sets of water softeners.

Two or more sets of the water softeners provided with control valves 11 for switching flow passages are serially installed. The control valve 11 is equipped with a first stop valve 17 at a first flow passage 16 connecting a water feed port 12 with a resin accommodating section 10, a second stop valve 19 at a second flow passage 18 connecting a water exit port 13 with the resin accommodating section 10, and a third stop valve 21 at a third flow passage 20 connecting the water feed port 12 with the water exit port 13. Further, when any one water softener is at water flowing work, operation is performed so that the first stop valves 17 and the second stop valves 19 of other softeners are made into a closed state and the third stop valves 21 are made into an open state.