To solve the problem that when a water purifier is fitted on a tip of a water output of a faucet, hot water is erroneously fed into the purification cartridge, and scales adherent to the cartridge are released and discharged from the purified water output.

The water purifier 26 which purifies city water and discharges purified water is fitted to the tip part of the water discharge port. In the upstream part of the purification cartridge 34 of the water purifier 26, a shape memory alloy spring 70 as a hot water detecting means for detecting whether raw water which is introduced unpurified city water is hot water or water and a hot water change-over valve 64 which changes over the flow of the raw water automatically from a purified water discharge channel 48 which passes through the cartridge 34 to a raw water discharge channel 42 which does not pass through the cartridge 34 on the basis of the detection of the spring 70 when the raw water is hot water are installed.