To detect the replacement time of a filter cartridge even when the filter cartridge is replaced with a different kind of filter cartridge in a water purifier.

The different kind of filter cartridge having a different service life can be fitted and the replacement time thereof is detected. The water purifier has a service life set by a flow accumulation setting part 29 for identifying the filter cartridge and setting the service life limit in terms of flow accumulation, a flow accumulation calculation means 38 for calculating the accumulated flow of water flowing in the filter cartridge and an information means 30 for informing that the replacement time of the filter cartridge has come when the accumulated flow reaches the service life limit in terms of flow accumulation.