To easily confirm clogging of a filter and replace filters.

A gas inlet 4 and a gas outlet 6 are opened in the outer surface of a housing 2, and a gas take-out passage 11 communicating the gas inlet 4 with the gas outlet 6 is formed in the housing 2. An inlet passage 7, a shut-off valve chest 9 and an outlet passage 10 are provided in order in the gas take-out passage 11. A cylindrical mounting member 26 is removably mounted on the outlet passage 10, and a filter 25 for removing foreign matter contained in gas is held on the mounting member 26.