A housing 11 has an upper annular inclined surface 14 and a lower annular inclined surface 15. An annular filter 20 accommodated inside the housing has the end surface shape matching that of the inclined surfaces 14, 15. When the housing expands and deforms in the axial direction by the pressure during actuation, the inclined surfaces 14, 15 cannot be easily deformed. Therefore, the gas is prevented from leaking from the abutment portion of the inclined surfaces 14, 15 and annular filter 20. As a result, the entire gas is discharged via the annular filter 20.