Abstract: There is provided a tap water purifier to be directly coupled to a faucet pipe, which includes a water purifying barel filled with a filter medium and a cylindrical valve body integral with the purifying barrel. The purifying barrel having opposite opening ends. The valve body is inserted in a cylindrical bore formed in a casing for rotation about the longitudinal axis of the valve body. The casing has tap water inlet port means, tap water outlet port means and purified water outlet port means formed therein, the tap water inlet port means and the purified water outlet port means opening to the cylindrical bore in the casing at an angular distance of 180.degree. from each other in the same axial position. The valve body includes first and second flow path means formed therein, the first flow path means being communicated with one opening end of the purifying barrel, the second flow path means being communicated with the other opening end of the purifying barrel.