PURPOSE: To permit a fully close engagement of the leg of a cartridge with its housing so as to ensure the sealing of an O-ring by providing a tapered inner part in a groove engageable with a cartridge filter.

CONSTITUTION: A cartridge filter housing A is provided with a tapered inner part 2 in its groove 1 engageable with a cartridge filter 6. A hole 3 is formed through the bottom part of the groove 1. As a result, a leg part 4 of the cartridge 6 is engaged so closely with the groove that an O-ring 5 can be sealed accurately. A disinfecting steam is introduced efficiently into the engaging part through the hole 3 and fine foreign materials remaining near the engaging part can be easily expelled. In this way the possibility of an improper disinfection taking place near the engaging part can be prevented.