Abstract: An apparatus for softening hard water, wherein a raw water pipe, a soft water pipe, a discharge pipe and a salt water pipe are connected with a cylindrical valve seat equipped on a softening tank accommodating ion-exchange resin to open into said tank, a rotary valve whose center hole slidingly fits on the upper end of a water pipe erected through the layer of said ion-exchange resin is rotatably installed in said cylindrical valve seat, said rotary valve is provided with a passage through which said raw water pipe, soft water pipe and discharge pipe can be separately connected with said water pipe and a passage through which said raw water pipe, discharge pipe and salt water pipe can be separately connected with said softening tank without recoursing to said water pipe, and through the rotation of sai rotary valve the combinations of (a) raw water pipe and soft water pipe, (b) raw water pipe and discharge pipe and (c) salt water pipe and discharge pipe can be alternately connected with the softening tank, wh