In the present pretensioner, press contact portions are formed further to a side of an open end of a packing housing section than central portions of opposing faces along a depth direction of the packing housing section. Accordingly, when a packing is being fitted into the packing housing section, no great resistance is imparted to a curved face side of the packing from a press contact wall of a housing section body and the opposing face, and the packing is fitted comparatively smoothly therein. Consequently, even when fitting the packing into the packing housing section, a packing main body is largely resilient-deformed, such that a large collapse in a through hole can be prevented, and the sealing ability of the seal due to deformation of the packing main body can be effectively enhanced.