PURPOSE: To provide a water purifier for purifying service water and the like to remove harmful substances to a human body, but for retaining minerals required for the human body such as Ca++ and Mg++ and cutting off the polymerization of water by irradiation with electromagnetic waves in the far infrared ray zone.

CONSTITUTION: This water purifier is provided with a membrane filter with ultrafine pores and collecting impurities out of service water or the like fed by the reverse osmosis pressure and an electromagnetic wave emitting substance emitting the electromagnetic waves having the wave length of the far infrared ray zone and a useful metal element containing substance, and also a mineral filter 20 applying the electromagnetic waves to water from which impurities are removed by the membrane filter 10 and supplying ionized useful metal and an impurities discharge section 90 discharging the impurities collected by the membrane filter.