The present invention provides a water purifier, the water purification capability of which can be maintained over a long period of time. The water purifier 1 has: an attachment main body 10 that has an inflow passage P11, into which tap water flows from an inlet 11, and outflow passages P12 and P13 communicating with outlets 12 and 13; and a water purification main body 20 that has a first flow passage P21, a second flow passage P22, a third flow passage P23, a first filter material 25 between the first flow passage P21 and the second flow passage P22, and a second filter material 26 between the third flow passage P23 and the second flow passage P22 and is rotatably mounted onto the attachment main body 10. During a parallel filter material mode, the first flow passage P21 and the third flow passage P23 communicate with the inflow passage P11 and the second flow passage P22 communicates with the outflow passage P12. During a serial filter material mode, the third flow passage P23 or the first flow passage P21 communicates with the inflow passage P11 and the first flow passage P21 or the third flow passage P23 communicates with the outflow passage P13.