To detect the exchange time of a filter cartridge even when the filter cartridge is changed to a different kind of filter cartridge in a water purifier.

The different kinds of filter cartridges each having a different service life can be connected to the water purifier and the exchange time of the filter cartridge is detected. The water purifier has a life end point integrated flow volume setting part 29 for identifying the filter cartridge and for setting the life end point integrated flow volume and an integrated flow volume calculation means 38 for calculating the integrated flow volume flowing in the filter cartridge. The integrated flow volume calculating means 38 has a flow volume measuring means 27 and an integrated flow volume storing circuit 41. The integrated flow volume storing circuit 41 is initialized when the life end point integrated flow volume is set.